Ashley might not have watched as much anime as Hanma or Greg, but she'll catch up eventually, darn it. Also, for anyone unaware, what Susan is wearing is based on Japanese male school uniforms.
I generally prefer to think of Ashley's appreciation of Susan being more of a platonic "she's so cool" perspective than anything else, but put Ashley into a situation like this with her, and, well... Yeah.
Also, I'm sure Liz is just talking about studying.