I have 3 babies in a 10gal. All of them are active, moving around in the day. BUT, i have one that likes to come out after dark... Dunno why.

If you want activity (of course you do) I think the bet way is make her feel comfortable and secure. If she feels safe, than she'll probably be put more.

Have you been handling her? Being new, that may stress her out to the point where she stays hidden. Is she really jumpy and skittish near you? If so, that may be the problem. She's still nervous about you.