$29.99 for a Ball at Petco? Erm, wow. Have you asked why she was so cheap? You won't be able to find them that cheaply even at a herp show.
When you say she hasn't gotten rid of it, what do you mean? Does she still have flakes of skin on her? That's not uncommon for balls, they'll occasionally get that. It's not just humidity that can affect them; sometimes it's also stress and diet. Unless she continues this pattern for a few months or has kept her eyecaps, I wouldn't worry too much.