I actually found there to be a decent amount. There are Githyanki dialogue options with every third or fourth NPC it feels like. Sometimes multiple.
As for Lae'zel's approval, I dunno. Just being a Gith and saying Gith things shouldn't make her approval go up too much. For the most part you're just behaving like any normal, sensible person should behave from her perspective. You need to go above and beyond to impress her. Or do something to back her up specifically.
Plus it'd be kind of OP socially if you got approval from her every time you said something githy. Then you could make big decisions in a completely ungithy way and she'd still love you after.
