Sounds like you need to take She-Ra to your vet for a full exam. If you've tried treating the worms with over-the-counter meds, forget it. That stuff is very mild and doesn't work on many parasites. Your vet can recommend specific tests to check for thyroid function, cushings disease, and lots of other things that may interfere with fertility.
If you have wormed your dog and she still has internal parasites, then you need to let your vet know. Like Jaybay said, if you have been using over the counter meds, they are so mild you might as well not even be using them. It's best to spend the money to go to the vet to have a fecal exam done, and then let him give you the right wormer for whatever is found during the fecal exam. It's less expensive in the long run, and certainly healthier for your dog because the longer you mess around with inferior wormers, the longer your dog has an infestation of internal parasites and the further down it will drag her.
With regard to breeding, I wouldn't consider breeding her until you get a definitive diagnoses as to what is preventing her from gaining weight. Remember that things like thyroid problems are passed along genetically, and you stand a chance of producing puppies that all have the problem as well, even if you do eventually get her to conceive. It is far more responsible to just not breed a dog like this than it is to go ahead and do it anyway, because you will be sentencing the resulting puppies to lives with thyroid problems and you will be sentencing their future owners to a life of having to buy prescriptions for their dogs every month.
I would have a full physical exam done, along with full blood panels and have her hips X-rayed (Penn Hip is the one everyone is registering with these days, from what I gather), and then contact her breeder and find out if there are incidences of any of the following in any of the dogs in your dog's pedigree:
Osteochondrosis dessicans (OCD)
Von Willebrand's Disease (a bleeding disorder similar to hemophilia in humans)
GDV (Gastric Dilation Volvulus) or Bloat
Sub-aortic stenosis (a common form of heart disease in Rotties)
Eye problems (entropion, ectropion, progressive retinal atrophy)
All of the above are genetically carried problems that are common in Rottweilers, so before you breed, you owe it to your future puppies and their future owners to do your homework and find out if any of these problems exist in your dog's line. If they do, then as much as you might want to breed, it's only going to be problematic if you do. Even if your own dog is not exhibiting any signs of these things yet, keep in mind that most genetic problems do not manifest themselves until the dog is four or five years old or even older.
I know it sounds like I am trying to discourage you from breeding, and there is a grain of truth to that. So many breeds are overbred these days, and Rottweilers is one of them. too many people breed them just to produce puppies, and they don't give a second thought to what the outcome might eventually be. All they see are adorable little bear-like puppies running around in their mind's eye, but after those little bears grow up, too many times problems ensue that can end up costing people thousands of dollars to correct or maintain, not to mention that many of those problems result in dogs living with varying degrees of pain or discomfort. So please do your homework well before you embark on this journey.
Try using a horse wormer called ivermectin. You can get it from TSC or online. You give it by weight monthly. Then start feeding a high quality dog food with a good fat/ protein content. Try mixing 2 dog foods if you need too. Also, make sure you treat your yard for parasites. There are many options, check out some of the homesteader websites or the natural remedy websites for a more natural way to clean your dog's area. This will be safer for you dog then some of the chemical treatments. Also, feeding her eggs and cooked chicken will help, but make sure it is well done. If you add a little garlic to it, it will help prevent fleas too. Make sure you do not feed human food more than once a day. Also, feed her dog food twice a day.
I am not a vet but my husband and I have been training and helping dogs reach there full healthy weight for over 16 years.
I hope this helps!