Laezel is evil, though, as most githyanki are. They are a supremacist, xenophobic race, which view others as their lesser, and whose society is sustained by raiding other worlds.
None of that makes her evil though.
Heck, you can literally use the same description for humans IRL. Does that make every human inherently evil? Are YOU evil?
Lae'zel shows time and again, she is significantly less "Evil" than others of her race. Literally, from the moment you meet her and she DOESN'T just cut you down where you stand.
Beyond that, she allies with you to go looking for the creche. Since she actually gives a damn about life despite the harsh societal values imprinted on her from birth. Any other Githyanki would simply kill your party and go find the creche on their own (Or fight everything they can find looking for a worthy adversary to kill themselves on).
Even when she has a disagreement with Shadowheart. Not only does she NOT kill her (If you pursuade them not to kill other) but then agrees to become amicable with someone she hates. Again, showing that she's not a ruthless murder frog like Githyanki are raised to be.
Lae'zel is a character, who much like Shadowheart, is a caring and sensitive character trapped within a brainwashed hostile shell. Lae'zel is trapped behind the Githyanki upbringing which is a cold, crass and ruthless society. Shadowheart is trapped behind the Sharran ideology which is all about hating on Selunites and being dicks about it.
