Some great tips above, just want to add a few things:
Another reason it's important to remove the wheel is because the pups can get stuck in the wheel without mama noticing, and if she starts running ... well, that's not going to end well for poor baby.
Do not try to watch the birthing process. Yes, it's fascinating, but it can really put a lot of strain on the mother. Ideally, a day before you expect her to give birth you should move her to a dark and quiet room where she can give birth and look after the pups in peace, for a week or two.
Good high protein foods include poultry, tofu, boiled eggs, bread dipped in milk and kibble. Refrain from feeding unhealthy fatty/sugary foods, as you would normally.
Remove the father, if you have not already, as they can mate again straight after birth and this really isn't healthy.
You don't necessarily have to limit the amount of time you get her out for, just don't play with her if she really doesn't seem keen. It will cause unnecessary stress for mama.