Spaying a Maltese

My vet, who I'd trust with my own life, my child's, and my pup's, said to wait until Lucy was over 6 months, with 9 being preferable.(She weighed about 5 lb when I took her in and was about 9 mo). If you read a book on when dogs go into first heat, it is usually sometime after the 6th month or later. My son's Aierdale went into heat before he had her spayed, and she was 10 mo. Get a second opinion on this. Certainly she is in no danger of getting pregnant now and waiting won't be an issue for a while.
I have both a male and female tea cup size maltese. My male was neutered at 4 months and only weighed 2 lbs. Today he is full grown and weighs 3 1/2 lbs. I just had my female spayed at 8 months and she only weighs 2 3/4 lbs. She did far better in post-op than the male did. My vet is of the opinion ( and I have spoken to several) that years ago they waited until the dog was at least 8-9 months but that is not the consensus anymore. My vet does them beginning at 4 months. Good luck.
Pat