Adventuring with Mizhena in Baldur's Gate 1 (caution for the faint of heart: contains one written curse word, which is something you'd read in reference to the goddess of the Temple of Umberlee in-game anyway): https://www.youtube.com/watch?v=7vYksSIj17Q
I skimmed through this one and it has quite a few problems:
1. The letter seems to describe a "cure" for being transgender. This is extremely offensive; what would you think about a "cure" for your manliness? (I am assuming you are male from your username; if I'm wrong, feel free to correct me.)
2. Mizhena would not willingly put on the belt. If it's identified, she would refuse to put it on with an angry message. (This could be done with a script; remove the belt from her inventory and remove the gender change effect.) If it isn't identified, she would get very angry and would likely attack your party. (BG2 has many instances where party members would start attacking each other, so this could easily be implemented.)
Anyway, if that scene were from the actual unmodded release, it would be rightly criticized for being transphobic.