Hello, I'm Dr. Chris Smith and I'd like to help!
Pregnancy in dogs lasts 63 days or so. If you take her temperature rectally every day, at some point you will see her temperature drop by approximately 3 degrees from normal. At that point she will probably have puppies within 48 hours, sometimes a little longer.
The thing we watch for most is if she is in labor, and pushing to have a puppy, she would have it within 30-45 minutes, at the most. If she is going longer than that, she may need help from a vet and possibly a caesarian section (c section)
I would feed her a normal high quality adult dog food for now. Over supplementing her while pregnant can actually be harmful. Use something like Science Diet or Eukanuba.
With regards to exercise, I would give her regular exercise such as walks on a leash but I would avoid strenuous activity. Malamutes have such a thick coat, it is easy for them to get heat stroke in the summer.