I wouldn't take her bemoaning a lack of personal development as a strong desire to change disciplines. It was used to hint at the idea, yes, especially as that's exactly what we're getting with Alphinaud. In universe, she was mostly just annoyed at being relegated back to her old outfit while everyone got new shiny stuff. Plus Yoshi hinted at her new outfit (Or rather who she gets it from) having story significance so I'm sure she'll get her "personal development" moment.

Besides, Red Mage suits her very well, in my opinion, it'd be a shame to change that just for the sake of it. Sage will suit Alphinaud very well, though so it'sa decent change. During the reveal trailer I thought the animations seemed very suited to him.