Terrible idea. She's far too old at six to be having a first litter plus the SA and the fact she's a rescue/private rehome (unless I've read your posts wrong?) make her a completely unsuitable candidate for breeding anyway.
This from the KC site is worth reading though in case you're still considering:
If you are contemplating dog breeding, there are certain questions that you will need to ask yourself before proceeding:
Have I the time to devote to a litter until the puppies are old enough to go to their new homes, which is usually around eight weeks?
Am I knowledgeable enough to advise new owners about the various aspects of caring for their puppies, including rearing, diet, training and health problems?
Can I afford to pay for the recommended health tests for the bitch prior to mating her and, where necessary, her litter?
Do I know enough to help the bitch during the whelping, if necessary?
Can I afford to pay for a caesarean should the dam have difficulty whelping the litter?
Could I cope with a very large litter e.g 10 or 12 puppies?
Do I have sufficient knowledge to rear the litter correctly, including on worming, vaccinations and socialisation?
Would I be able to find good homes for the puppies?
Am I in a position to take back or re-home any puppies if it becomes necessary?
If you have not been able to say yes to all of the above questions, then dog breeding may not be for you. You may therefore wish to consider having your bitch spayed to prevent unwanted or unplanned pregnancies; your breed club or the breeder of your bitch may be able to provide you with further expert advice.
If you have been able to say yes to all of the above questions, do not forget that you will also need to keep the following in mind:
Responsible dog breeders believe that each litter that they breed, should be an improvement on the parents.
Responsible dog breeders give careful consideration to health issues, temperament and soundness.
Responsible dog breeders plan ahead of each mating so as to ensure that each puppy produced will be bred in the best possible environment.
Responsible dog breeders accept responsibility for a puppy which they have bred, and make themselves available to give advice, help and information to new owners.