Could be something in the wet food doesn't agree with her. Is it a new brand you haven't had before? I'd still call the vet, but take away the wet food and just let her have dry at least until after you talk to the doc.
Call your vet and ask his/her opinion on whether Molly should be seen or not. When in doubt, have her checked out. Bassets are notorious for getting into things they shouldn't and a foreign body in the GI tract could produce intermittent vomiting. Probably nothing but certainly worth asking the vet.