I look at it this way. Panties, and other aspects of my feminization, that I haven’t shared with her, of course, make me feel girly. That’s why I do it.
So, naturally, even when it’s just panties, perhaps she senses this.
Since she is not attracted to women, not even in the slightest, when she senses some tiny change from my male self, it’s a turn off.
At least, that is all I can assume is going on.
Maybe some SOs can chime in.