If she's worth her name to be in Eros, Cityvibe, or the others, it's like a standard tool she should have them already. Part of the business equipment!!

Every now and then you'll run across a provider that forgot to bring them, so its good to have your own as a back up.  Doesn't happen that often but when it does, it's usually a pain in the ass to interrupt the session, get dressed and run to the store.