I think by アマ!イボ!ガマ! she means to point out that there are different kinds of frogs. アマガエル, イボガエル, and ガマガエル.
雨蛙 (あまがえる) = tree frog (esp. the Japanese tree frog, Hyla japonica)
疣蛙 (いぼがえる) = toad with wart-covered skin (esp. the Japanese toad or the wrinkled frog)
蝦蟇蛙 (がまがえる) = [another kind of frog, possibly similar to いぼがえる. I'm not sure]
I can't make out all the kanji in the scan, but it seems that there was some kind of discussion, in which Ruka claimed that Medaka (it's a kind of fish I think) turn in to frogs, but Kaede seems to say that frogs are always frogs. At which point Suu-chan threw in that there are three kind of frogs: Ama(gaeru), Ibo(gaeru) and Gama(gaeru).
Feel free to correct me though …