I also didn't know that the dog goes into heat at the same interval, hmm.. (I thought the cycle "begins" anew after they whelp, I am new to this, learn something new every day!)
It will take its toll on her little body, so make sure you give her lots of very high quality food. Her body's nutrient stores are probably still low from nourishing her last litter. I have heard of people breeding back-to-back-to-back, over and over, because they are money hungry
and those dogs survive. They're usually scrawny and weak but they survive. But the good news is, your dog is probably a lot healthier than these dogs. Under a vet's watch I bet she will be ok. Good luck!