Are you serious?? Maybe you should talk to your Dad about this egregious offense to your spiritual sensitivities and see if he can talk some sense into her.
Regarding the “issue” itself, there is nothing you can do about it even if it was an issue. Also, this is clearly not a big deal so lay off. It’s not like your mom is parading around town in a bikini. And even then, there is not much you can do.