These things happen. I too didn't know my female went into heat and she mated with a 6 month old male yorkie that I was watching. I went back and forth about terminating the pregnancy or not. After talking with my Vet and several check-ups, I decided to let her have the puppies. She is due at any moment any day now. She has been very active, happy and healthy throughout.
So talk to your vet and get their opinion. You stated she is 7 lbs and the father is 4lbs. It's not an ideal situation, but personally don't think you will have any problems. Best of luck too you and your girl!!!!
