You will need to sign over the title to the car, give her the cars registration card and do write up a bill of sale for the dollar amount to make it official. Here is a more detailed Link on what you need to know with a BOS you can use.
Thanks @john65pennington I guess we should add that even when giving a car to someone you have to do all of the above and best to “give” the car for at least a token one dollar written in the BOS. Or at least that was what I was told to do to make the exchange a legal transaction.
Give her a bill of sale and sign the title over to her. The rest is really up to her, but if I were you I would follow up to make sure she has registered the car into her own name. Also, let your insurance company know you have sold the car.