How to Recruit Jaethal
An elven hedonist who was exiled from her homeland of Kyonin for the despicable crimes she committed against her own family. During her aimless wanderings after her exile, she came down with a slight case of death, the cause of which is still a mystery to her. Whatever the cause, she's now an undead in service to the goddess Urgathoa, although she's not entirely satisfied with the lack of sensation that has come with her undeath.
Coming armed with a scythe, Jaethal seems primed to fulfill the role of the undead, unholy inquisitor quite well. Her high Strength and Wisdom and passable Dexterity (suitable enough for medium armor) ensures her attributes don't disappoint. That said, abandoning the scythe for a one-handed weapon and shield will probably serve her better in combat at least in the short term, and one has to be mindful that her Base Attack Bonus won't be as high as a proper warrior's. All in all, she'll perform admirably as a secondary warrior who can also cast a few spells in a pinch, but she's not a substitute for a primary warrior or a healer.
One should also keep in mind her undead traits, which complicate matters somewhat. Jaethal, as an undead being, cannot be healed by normal healing magics. Healing spells like Cure Light Wounds will instead harm her, but on the other hand, damaging spells like Inflict Light Wounds will heal her. In addition, Jaethal's Constitution score cannot be modified, and doesn't contribute to her Fortitude Save or HP. Instead, she uses her Charisma score for these purposes, so keep that in mind when divvying up gear. On top of that she's immune to bleed, death effects, disease, paralysis, poison, sleep effects and stunning. She also can't be permanently killed in combat, but she can still be disabled by having her HP reduced to zero, and her undying status won't keep you from getting a game over in the event of a party wipe.
As an Inquisitor, Jaethal gains access to a variety of useful abilities, including a variety of Judgment abilities that, when activated, can do anything from regenerating HP, increasing attack, damage, armor class, saving throws or physical and elemental resistances. She also gains access to a mix of divine and arcane spells, although her progression is slow and her selection is limited (like a Sorcerer). These spells are nevertheless useful, ideally including common buffs and healing spells, allowing Jaethal to serve as a secondary caster.
Every skill is a class skill for Jaethal, and she actually gets enough skill points per level to meaningfully progress in several skills simultaneously, making her an even more useful addition to any party. Considering she receives decent attribute modifiers due to her Strength, Dexterity, Intelligence, Wisdom and Charisma scores, she can excel in many things, but you should be especially keen to invest in Perception, as her elven senses and high Wisdom will give great bonuses to this skill. She is, in fact, the premier character to use for such things, barring a specialized protagonist. Other than that, use her to bolster whatever skills your other party members don't have, just be wary that her Athletics, Mobility, Trickery and Stealth will all be hindered by any armor or shields she's using.
Jaethal is arguably the third best warrior companion you get, on top of which she possesses unique undead traits, a small but useful spell arsenal, and a wide variety of skills, making her a good utility character for any party.