dvoraks
Very nice for you that she is so willing to try it out. But I assume only within the safety of home, and not e.g. to school.
I'm not sure why she would like them, though. I can imagine she might like the idea of being chaste, if that is an important value in her upbringing, and that it makes her feel like she is a big girl now, wearing what mommy wears. But I don't think anyone would consider them more comfortable than a normal pair of panties, especially not if they are not made to her exact measurements, and accept all the inconveniences only because they look good.
For now it of course is mainly trying out something that mommy wears. So I expect that sooner or later the novelty wears off, and she will probably tell you she is no longer interested in wearing them. Perhaps after a few days, weeks or months, when she realizes all the other kids talk about how great masturbation is, and she can't even try. How will you react then? Will you be telling her "Too late now. You've made your choice and now you'll be stuck in them until your marriage"? Or will you just let her out again, and try to get her in again at a later age, when you planned to get her belted anyway?