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. ... If you are familiar with githyanki, there is little reason to trust Laezel in the beginning of the game. Because even if her people had a cure, it is very unlikely they would offer it to an outsider.
But Lae'zel never betrays you, she trusts your judgment even if you doubt her or her knowledge. Also by your logic, every race is racist. So therefore, we shouldn't trust anyone!
And while I am not extremely familiar with the githyanki, I have reason to trust Lae'zel because she knows what she's talking about regarding the Creche and what solutions the party can seek. She's not evil because she allies and travels with you despite what she knows to do, she is willing to go along with friends and potentially help them figure out answers to the parasite. Like Taril mentioned as well, she doesn't kill you from the beginning despite that might be what other githyanki do. She is remarkably one of the least evil members of her race.
Like a lot of people both in fiction and real life, Lae'zel is just another person who grew up and was raised in the mindset of kill first, questions later. But she is much beyond that when you meet her at the beginning of the game and even helps get you out of the nautiloid alongside her.
So no, Lae'zel is not evil, and she does experience character development and sees past the murderous ideals of the githyanki.
