I'm going to re-iterate what everyone else said. A 20 gallon tank is probably going to be too big for her now. There are alternatives to glass tanks, and that's tubs.

I don't set up babies in anything larger than a 15 quart tub. Ball pythons are very shy by nature, and a baby even more so, since they are more prone to predators. Just because it's in captivity now, doesn't take away that instinct to lay low and find the smallest, tightest area that they can.

As mentioned above, you need two identical hides, one on the cool side, one on the warm side. They need to be as small as possible, so that it is touching your snake on all sides (including the top) when it's inside it, otherwise it really isn't providing much security for your snake.

A pinky mouse is much too small, even for a baby. Try a live hopper mouse (eyes just open) next time. Also, you should wait a full week before offering it, it's first meal. It needs a full week of no handling before offering feed.

I feed IN the enclosure for all sixteen of mine. I've never been mistaken for food.

Here's what my baby tubs look like (and this baby was eating mouse hoppers, by the way)