Yes that is a perfectly acceptable sentence.

"She is recovering from anaesthesia." tends to imply recovering from an operation after a general anaesthetic. We tend not to use the word anaesthesia so much when talking about the dentist. "Recovering" also sounds too drastic, i.e. coming back to consciousness. I think hmano's suggestion is a good one, i.e. "the numbness is wearing off". An alternative would be "waiting for the feeling to return".

Thank you, hmano.

Sorry:) The numbness IS wearing off.

Perhaps: The numbness wearing off.