I've got a couple of suggestions for changes here.
However, since (he/she) wears a mask, no one knows (his/her)
"There are few who know his/her alter ego or have seen him/her unmasked."
"A sweet girl who loves animals and nature. She was living with her father deep in the forest. However, she had a few slight problems
. She had grown large horns and a splendid set of wings, and just recently, she had gained the ability to control fire."
I think it's best to just use "love" here. Anything else sounds pretty forced and unnatural IMO. Though I guess it might be OK to use "a sweet girl with a great fondness for animals and nature".
Also, here are a few thoughts on (大)好き versus 愛する. As other have already pointed out, 愛する carries more serious connotations than 好き. For example, my wife and I say 好き to each other multiple times a day almost as a greeting, but we only use 愛する when we're talking seriously about our commitment to each other or to our family.
On the other hand, though, 好き can sometimes be taken as more serious than 愛する. As awkward as the situation probably was between geishaboy and his co-worker, it would have been weirder had his co-worker said 好きだぜ. By saying 愛してるぜ, he was obviously exaggerating, but if he'd said 好き, it could've been taken as serious because it could have been more plausible, depending on the way in which it was said. Although I'm guessing that either phrase would've been uttered in a drunken shout, so the effect might actually have been the same either way.
tl;dr: I guess you could say that 好き means "x makes me happy", and 愛する means something like "I care for and am deeply committed to x". So, Character 2 probably doesn't just like to play with animals (好き), but she likes to care for them as well (愛する).
One more thing about the character bios. In general, the info at the end about favorites and catch phrases should probably look as follows (i.e. as labels and colons instead of sentences):