The size of your girl and the male used for breeding alone means little. You have to take into consideration the sizes of the
other dogs in their lines as well. Also, have the females in her line had an issue with free whelping?
In addition, more so than her actual size/weight, her pelvic structure has to be considered as well. It's not at all unheard of for a larger 6-7 lb female to have a narrower pelvic structure that would make breeding risky. Personally, 4.5 lbs is really borderline and risky, IMO.
I think that the advice given regarding finding a mentor (if you don't already have one) is the best advice. A well seasoned breeder will be able to help you evaluate her in this instance way better than anyone here could.
You didn't give her age...perhaps she still has a bit of growing to do and may get a bit larger?
I do want to give you kudos for having her thoroughly screened though.