Please Help!

[shellymonica]

Can someone please tell me what is wrong with my little frog?
She's an African Dwarf Frog. Today I noticed her arm was encased in some "stuff" and her arm is pinker than the rest of her. It wasn't like this yesterday. She was in a tank with another African Dwarf Frog and 2 Bala Sharks. When I noticed her arm I moved her into her own little tank until I can figure out what to do. This isn't the best pic, I know, but the affected arm is the one on the right (her left). What do I do?

[Ted]

Hard to tell but it looks like fungus

[shellymonica]

What do I do about that? How does it happen? Did she get it from my tank or from the pet store tank? We only just got her 4 days ago.
How can I prevent it from happening again? Is she going to be ok? Is it painful for her?
I apologize for the 20 questions but I REALLY want her to get better.