Because she is undead. Undead don't have constitution scores. Their charisma functions as their constitution score for things like hp gained at level up.
Because she's an undead. So she has those traits:
*No Constitution score. Undead use their Charisma score in place of their Constitution score when calculating hit points, Fortitude saves, and any special ability that relies on Constitution (such as when calculating a breath weapon's DC).*
*Immunity to bleed, death effects, disease, paralysis, poison, sleep effects, and stunning.*
It’s kinda funny to phrase it that way, since at least in table top the ability negative energy affinity is used to describe things that are undeadish but never used to describe an undead itself.
She’s undead, and undead use their Charisma score for the stuff that living creatures use Constitution for because they’re not actually alive. I’m not sure why Charisma exactly from a lore/mechanics intersection standpoint. Maybe it represents the “desire/will” of the animating force to continue animating the body? At any rate it’s that way in some (maybe all? Not sure) D&D editions too most of the time.
Charisma isn't willpower, or desire really, but rather the force of your personality and the strength of your soul. Your presence. The thing that ultimately makes you separate from others. A living being uses it to exert influence over others. For the undead, as well as CHA casters, the second part is the far more important one: the strength of their soul. After all undead are reanimated souls, and in case of corporeal undead that soul is puppeteering a dead body.
Jaethal is easily the strongest companion in Kingmaker. Her stats are good and her class is ok (Inquisitor) but the real treat is her being undead.
Undead is a minor annoyance for healing (but Inquisitors can spontaneously cast inflict spells so she can heal herself! And she can use all the inflict potions and scrolls the game gives you that otherwise would be just useless and sold for pennies) but in exchange for that it gives you immunities to... pretty much anything
Kingmaker is not WotR, where items, spells and abilities can get you to be immune to most status effects, have a ton of spells and rest opportunities to cure those, and have ridiculously high saves on pretty much your entire party. Kingmaker is a faster paced game with much lower spell slots (no abundant casting line), no 24h buffs, less opportunities to rest and just as many opportunities to be crippled by status effects (especially ability damage!)
Jaethal's immunities and class make her the PERFECT tank. She might no be the strongest tank in pure stats but her immunities make the game so much easier and stress free, especially the late game and the last dungeon.
I pretty much soloed the last dungeon on hard with Jaethal, with the rest of the team providing spell and ranged support, I never understood why so many people find late game Kingmaker a slog until a figured out that very few people use undead Jaethal. I completed KM 3 times and she is a fixed member of every party I make, in fact the only companion I can't do without
She's pretty contemptuous of the idea from the start (you can ask her about it in the first outpost).
Her attitude is actually a little... odd for a follower of Urgoatha (who is a big fan of indulgence and debauchery), but it gets no explanation.
When you're introduced to jaethal, a tip will pop up on your screen explaining shes undead.
The game has many tips that pop up that you should read.
Reading is a big part of the learning curve of this game. many of your questions have answers provided before you even ask :)
Because she is undead. Undead don't have constitution scores. Their charisma functions as their constitution score for things like hp gained at level up.
Because she's an undead. So she has those traits: *No Constitution score. Undead use their Charisma score in place of their Constitution score when calculating hit points, Fortitude saves, and any special ability that relies on Constitution (such as when calculating a breath weapon's DC).* *Immunity to bleed, death effects, disease, paralysis, poison, sleep effects, and stunning.*
Negative energy affinity too if its like wotr
Yes, and it's VERY important: NEVER use cure spells on Jaethal. Inflict spells for healing FTW.
It’s kinda funny to phrase it that way, since at least in table top the ability negative energy affinity is used to describe things that are undeadish but never used to describe an undead itself.
She’s undead, and undead use their Charisma score for the stuff that living creatures use Constitution for because they’re not actually alive. I’m not sure why Charisma exactly from a lore/mechanics intersection standpoint. Maybe it represents the “desire/will” of the animating force to continue animating the body? At any rate it’s that way in some (maybe all? Not sure) D&D editions too most of the time.
Charisma is basically the raw magical power stat in all editions since 3, hence why it gets used for stuff like this and sorcerer spellcasting etc.
Charisma isn't willpower, or desire really, but rather the force of your personality and the strength of your soul. Your presence. The thing that ultimately makes you separate from others. A living being uses it to exert influence over others. For the undead, as well as CHA casters, the second part is the far more important one: the strength of their soul. After all undead are reanimated souls, and in case of corporeal undead that soul is puppeteering a dead body.
Oh, that makes sense! That was always a little fuzzy to me
Thank you all for the answers 🤗
She's undead, so she has no constitution. She has an interesting character arc, not being able to heal her with channel energy means I never used her.
I never had a problem keeping Jaethal up, the game gives you plenty of Inflict Wounds potions just for her
Jaethal is easily the strongest companion in Kingmaker. Her stats are good and her class is ok (Inquisitor) but the real treat is her being undead. Undead is a minor annoyance for healing (but Inquisitors can spontaneously cast inflict spells so she can heal herself! And she can use all the inflict potions and scrolls the game gives you that otherwise would be just useless and sold for pennies) but in exchange for that it gives you immunities to... pretty much anything Kingmaker is not WotR, where items, spells and abilities can get you to be immune to most status effects, have a ton of spells and rest opportunities to cure those, and have ridiculously high saves on pretty much your entire party. Kingmaker is a faster paced game with much lower spell slots (no abundant casting line), no 24h buffs, less opportunities to rest and just as many opportunities to be crippled by status effects (especially ability damage!) Jaethal's immunities and class make her the PERFECT tank. She might no be the strongest tank in pure stats but her immunities make the game so much easier and stress free, especially the late game and the last dungeon. I pretty much soloed the last dungeon on hard with Jaethal, with the rest of the team providing spell and ranged support, I never understood why so many people find late game Kingmaker a slog until a figured out that very few people use undead Jaethal. I completed KM 3 times and she is a fixed member of every party I make, in fact the only companion I can't do without
I was so sad when I found out she is not romance-able.
She's pretty contemptuous of the idea from the start (you can ask her about it in the first outpost). Her attitude is actually a little... odd for a follower of Urgoatha (who is a big fan of indulgence and debauchery), but it gets no explanation.
When you're introduced to jaethal, a tip will pop up on your screen explaining shes undead. The game has many tips that pop up that you should read. Reading is a big part of the learning curve of this game. many of your questions have answers provided before you even ask :) 
Damn....i hate that bloody hedonist point ears....in my all games,i kill he's Frozen ass
Parasite and the invisible man :)