Agreed, I have known quite a few women including my own mother that happily walked around at home when alone with the family just in very short bathrobes especially during the summer, it is not that uncommon outside of prudistan and especially if have been doing so for years and years does not mean anything.
Now here in game that can be slightly different since Marge has been working hard on her body and MC is the only one she wants to notice, so it might well be a part of her change/what is going on with her personalities. Just a simple remark off MC though that she has done so since he was a little kid but notices more now how good she looks or that it is a new thing could give that some context without needing a big change.