Oddly enough, I never really thought of this. I generally just make the decisions as I go along, mostly in line with what I would personally choose.
Pendalyn doesn't like the DB for sure. They have been hunting her and her family for years, so I guess she will never do that questline. She has little desire to be a faction leader. She 'accidentally' became the archmage, and is looking for someone to reverse pick pocket the robe too. As such, she'll never full complete most of the 'guild' faction story lines. Her father taught her sword skills, and he was one of the legendary Iceblades of High Rock, so she doesn't feel a need to seek out the companions. The civil war in skyrim means little to her, she doesn't have a favorite side, but is not a fan of Ulfric. She helped the king of the Forsworn, less by choice than by desire to leave the mine, but will gladly slaughter any forsworn who attack her.
Pendalyn doesn't fully grasp the whole 'dragonborn' thing still. She knows she has this dragon speaking ability and she uses it, but she's kind of playing a naive/innocent attitude towards the main She will kill all vampires she comes across. The Bretons fought wars with Vampires in the old days, and those skills were passed down to her. I generally help who I want to help, judging that by the NPC's personality. Right now, Pendalyn is still building her legacy. She has some plans to retire after the main quest, doing the radients and traveling from town to town under different guises. She uses potions and blacksmithing to make her money, much as her family back in High Rock did. She wants kids, and will likely marry some day, though she doesn't have prospects yet.
Pendalyn always falls back on shield and sword, but is well versed with a bow, and knowledgeable with magic skills (mostly destruction spells and healing, with a sprinkle of conjure atronoch). She prefers a tank (companion) because legendary is a hard mofo'in difficulty, and they can carry extra weight. When Pendalyn needs to sneak, she easily does so and leaves the help outside. Often she likes to take the sneaky route, shooting foes with arrows then hiding back in the shadows till she can sneak attack again. I'm trying to build her as a well rounded character (not worried about getting my main skills to 100), then focus on her barter, smithing and alchemy for retirement.