I've never had an African bullfrog or researched them much. I do know that they grow huge, mostly just sit there, and can eat large prey like mice, birds, etc. Here are some links I found. It looks like they're mostly feeding dead mice but, for smaller frogs, crickets, mealworms, waxworms, and earthworms should work.
http://www.anapsid.org/bullfrog.htmlhttp://allaboutfrogs.org/info/species/pixie.htmlhttp://www.honoluluzoo.org/african_bullfrog.htmThey don't eat too often (a single meal tends to be large though when older), and they can go for weeks without eating or defecating so I wouldn't worry too much about that. Eating a little tree bark shouldn't stop her up. I wasn't able to find a web site with photos of males and females but they say the females are much smaller. I'm not sure for this species if hibernation (or rather estivation) is a good idea but did read on that first link that the frog did sort of hibernate at times.