I have had two litters of 2. One litter was from a littler girl, just under 6 pounds, she did fine with her delivery, both pups in the 4 oz. range.
A bigger girl, 7 1/2 pounds, well that was a different story. She had the two biggest pups I have ever had (my monster babies). We knew they would be big from the x-ray so if you repeat your x-ray just a few days before your girl is due the vet should have an idea whether or not your little girl should have any problems with the size factor. So many other factors determine whether or not a c-section is necessary, puppy size is not the only one. Puppy presentation and size of the mama's pelvic opening, strength of contractions, etc. the list goes on.
Anyways, I don't want to scare you but I will tell you how big my monster puppies were, one was just over 8 oz. the other just over 9 oz. People tend not to believe me. Needless to say the mom did need a C-section, but she has become a legend in my vet clinic because the day before they helped deliver bearded collie pups that were actually smaller than hers.
We always pull out her x-ray so we can compare whenever one of my other girls is expecting just so we can say "well these look nice and small."
Anyways repeating the x-ray might be helpful to you.
Audrey