Like stated before in order for her to free whelp alot goes into the breeding:
Size of parents, grandparents on both sides.
Why did her mom need a section? Sometimes it is one reason but then the next time them free whelp.
The dogs frame especially in the pelvic region.
I do have a question for you though, you say she has long legs, tiny framed, and big ears yet you say you want to breed her? I am not trying to be mean, I just know the description does not sound very appealing but maybe she is gorgeous...
I would say medically ask your vet to xray her hips and tell you what he/she thinks first and foremost. Then evaluate her as breeding stock, does she fit the standard closely? Is she in great health? Are you prepared for a c-section and/or possibly losing her? Is the male you have a pretty close to perfect representation of the breed? Do they complement each other fault wise? There is so much to mating 2 dogs...Have you done that research? Pedigrees?