I have had to take prednisone on and off for years due to my phenominally crappy skin.
Unfortunately low carb is the way to go, I just started the v diet (day 3, lost 3.5 kg…wish the UFC wouldn;t advertise food) and its working seriously well (big ups to Chris Shugart for the diet and Avocado for the protein/green tea ice cream idea).
Despite the water retention she needs to be downing as much water as she can and she definately needs a calcium supplement as well and some vitamin E to help with bone density loss from the Prednisone. This is a big problem for women on prednisone, even more than for the guys so perhas her Dr can perscribe her a calcium supplement with some vitamin c and I ron along with it?
Weight training and some sort of appetite suppresant (HOT-ROX/se7en?) will also do her no end of good. because of its effects on water retention and appetite she does need to be very careful especially if its a high dose.
Something else i found was I became very depressed cycleing off prednisone and needed an anti depressant (fluoxitine) to keep me on the level, however when i went back I kept taking the anti depressan and I didn;t get the surge in appetite I got without the anti depressant.
Obviously get her to talk to a Dr about it but those are my experiences so far… sorry for the long winded approach I just know how badly this drug can hurt your system.