If this is her first heat it can last anything from two or three days to five or six, or even longer. Often the first heat is shorter. Yes, you can have them spayed in heat, but it may take a little longer because of the swollen blood vessels and therefore may cost a bit more. When this happened with my Persil (the vet was delaying her spay because she was recovering from other surgery) I kept her in a quiet and dark room for three days and then she went for a spay.