I believe she should be allowed to have a mixture of both wet and dry food because if that's what she's most fond of at this point, she should be able to indulge to keep her feeling stress free and satiated.
She needs to be fed an always ready and available supply of wet & dry kitten food. Kitten food is higher in nutrients and is good for pregnant, lactating or recovering cats.
Lactating or Pregnant cats need to always have food when they want it. They need to always be stress free or as close to it as you can manage.
The reasoning for this, is that you don't want her to stress enough she abandons them, and also - the better health & if she's getting good nutrition, then the less chance her milk will dry up. This is always a huge risk with thin or underweight new mother cats - so it's best for her to be able to eat her fill.
All my older cats get fed Optimum dry food. I never feed them the wet stuff. They're all healthy and happy, however when S, M & K had their babies they were immediately switched to the best wet food as well as some dry food available (avoiding whiskers at all costs!) & when F (S's remaining baby) started wet food, she was on the best wet food as well.
I would stay clear of the cheap, generic store stuff. I was a fool, when M's first litter were born, and fed them Whiskers & Snappy Tom & Kitty Cat & I was made to regret taking the easy route.
By the time they were 6 months, they were severely underweight, no matter what they ate, and one of them nearly died because it would go in one end and out the other, until the vet gave me royal canin and I realized what was wrong.
Royal Canin is the BEST FOOD ever. It saved my cats life, however, failing being able to find it or afford it, Optimum is good as well. Feeding them good food will help them in the future.
She needs to be able to eat as much as she wants and gain weight. When the kittens are born, if she's relaxed, in a nice, dim & warm place with enough time to bond with her babies, she should do fine with them.
Keep the babies away from your other cats as their immune systems are still developing. Make sure you keep the blankets clean and sanitized.
When kittens are old enough, get them to have a general vet check, and I'm sure you'll find good homes for them all.
This cat is lucky to have found you, it's sad that she was cold and stick thin and such, but hopefully you can give her all the love and care she needs and help her deliver her babies healthy into the world so that they can find future loving homes.
