Have you been reading the threads in the Food Forum? There are some good links there that you'll want to check, but I'll start you out here with a good one:
www.greatdanelady.com . There are even several articles there that address the specific needs of large puppies, and everything is presented in a real-world manner that is understandable and practical. After all, a feeding program doesn't do your dog any good if it's too complicated to use.
Getting her on a nutritious, non-toxic food will help her stamina greatly, too, as well as decreasing those St. Bernard puppy piles in frequency and size - a real help in housetraining!
Be careful about a puppy in the garage; even though she can't get into the things that are typically found in a garage, she still gets the fumes from those things. We can't smell them, but they are there and they aren't good for a baby. That's one of those things no one ever tells you about. If you keep your car, or any other type of motor or engine driven machinery there it's that much worse.