Just do it I had the same not so long ago and my mil is a very sexy curvy woman I can still smell them thongs now
And I kept one to a nice sexy pink one my bad lol
"So my MIL is currently using our washing facilities and has left some stuff here to dry. Soooooooo tempted to wear them but not sure." any sexy worn knickers in her stuff ? How old is she ? What size is she ?