Get a rather large flat dish and try normal earthworms that you can get at any wal-mart. They are large, rather cheap, have lots of minerals in them and will even my American toads can eat a couple in a sitting.
They also keep well in a fridge for quite some time, although a bull-frog should pound through 12 of them in two weeks easy.
On the other note, no heater needed for an American Bull-Frog. 65F is fine as most ponds never get much warmer then that.
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Just reread your post and noticed she was only a inch or so long. Try red worms instead, which should be in the same cooler at wal-mart. They last even longer then earth worms and are about 1/3 of the size. Once she gets about 2 1/2 inches she should be able to tackle earthworms.
Crickets would be a good feeder as well, dusted with some reptile calcium dust or mineral spray (you can get the stuff at any pet store). She'll need this little extra calcium and minerals to build strong bones. You can also just dust worms though.
Unlike with worms you won't need to watch her eat all of them and as long as you have a secure lid (which you should) with a bullfrog she can eat them whenever they come close to the water's edge.
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Bullfrogs get quite large, if Cali bullfrogs are anything like IL/Wisconsin American Bullfrogs. Once she gets 4-5 inches I'd suggest getting a larger breeder tank (40 gallons) which only runs $80 or so bucks on sale at most pet shops. This will give her a little more room to spread her legs to swim and leap. Full grown, spread out in a jump a bullfrog can easily measure 12 inches if not more.