First off, I think that is great that you are caring and want to help your friend. You sound like a great friend yourself.
Does she have family near by? If so, maybe you could set up a day for her family to take her kids and come and surprise her with a spa day or a mani/pedi. Get her out of the house for a few hours.
Even the smallest things help though. Just a phone call to let her know you are thining of her and talking to her later at night when the kids have gone to bed would be great. I know when MH was deployed, it was nice to just have someone to talk to.
Perhaps there is also some place in her area that does a "Meals on Wheels" type of program. Perhaps you could send dinner some night.