[mscat]

I agree with the others. A 5 pound little dog being mated with a much larger male , could present major problems during delievery. She might not be able to push out the puppies, and they could all die, even placing her at risk of death.
I would not take the chance of this happening. It is more a risk to allow her to give birth then a spay. 5 pounds is not too small for spaying. Years ago my female cat was pregnant, before spaying, she was already showing a little, and I chose to have her spayed.
Some vets charge a little more if the female is pregnant for a spay, or if the female is in heat.
I am sorry about what occured , it was not intential. Accidental pregnancies happen . This does not mean you are a bad pet owner. A male dog can smell a female who is in heat miles away... That is why a male dog will wander off , to find some loving...
I hope your female will be ok , this must be a hard choice to make.