this is a tough one, and something that is entirely up to you; hopefully all the information in this thread has been as helpful as you hoped it would be...
one thing i always have to remind myself of, is that breeding and whelping (deliberately and accidently) is an expensive and sometimes heartbreaking thing to do- i lost a 7 week old pup suddenly to an anurism about 3months ago and i still find myself crying about it now- and that'll be me for a long time over her, and if i ever loose any more
babys. i love my girls like parents love their children- (i'm assuming its the same with most furbaby owners) so loosing a little creature that you helped deliver into this world- the offspring of your much beloved pet- is a feeling that you cant really prepare for, and its made that bit more likely with such a close inbreeding as your new additions.
personally, i would take her straight to the vet, see if she is pregnant for starters- if not, get whatever is causing the oversized abdomen treated, if she is pregnant and you don't want to immediately spay, talk to the previous owner about it, get an idea of 'heat' dates if possible (maybe they noticed her staining the furniture?) and compare those dates with the x-rays of the pups to ensure the sire wasnt a larger breed dog, then ask the vets experinces with inbreedings, do Loads of research, talk to breeders in your area- maybe someone would be willing to lend a hand if needed; start buying in whelping and weaning supplies and saving up for vet visits and puppy shots etc... and try to arrange a way for someone to be there 24/7 with her as she gets closer to whelping time...
please let us know how it goes at her check-up!
all the best!