I played both male and female characters in my college D&D sessions, and in our last game, the DM let me play a beholder who was so insane, it had turned Chaotic Good. That was a blast!
Frankly, I think mothers like this are frightened at the fact their kids are growing up and becoming their own persons, which may not exactly line up with the mothers' expectations. The fear of transgenderism is a symptom of the bigger fear of losing control. Plus if their child does transition, it blackens the whole family's reputation.
Change is gonna happen, no matter how hard you fight it. Except now I really want a blue IKEA shark.