Hi TillyO,
Yes I have seen her doing this as well.
Personally I am not worried about it and in fact I prefer her doing it that way. They probably clean the earrings in between shows etc. My brother is a jeweller and he steam cleans a pair of earrings after they are tried on by a client. He says that it is important to really try them on as it gives the client an accurate feel of how the earrings look, how they hang, especially with drops, that the post is long enough on studs and where they sit on the lobe. When they just hold the plastic stick up, quite often the earring post is not sitting right on their pierced hole, so the viewers can't really see all of those things.
Whenever I buy new earrings, I clean them with a sterile wipe and that's fine for me.
Inge x