That is a pretty big enclosure for a BP. Since she is 3 yrs old, I do believe she'd be a little cramped in a 10 gallon, but she might prefer that to feeling insecure in that huge tank. Do you know how much she weighs? Depending on her history, a 3 yr old could still be pretty small.

Probably the best solution as far as being quick easy & inexpensive is to buy a plastic tub and set her up in that.

Are you having trouble maintaining the proper temps & humidity in that big tank? If so, I'd definitely ditch it. If not, since I am assuming she was in there the first few months you had her and she was eating ok, you could try to get her feeling more secure in her big home, if you wish. Add lots of stuff in that big tank to make it feel more secure to the snake. BPs don't like big open spaces; they'd rather be cramped. So try adding in a few extra hides and then fill the rest of the empty space with something like crumpled newspaper or fake foliage.