Is there any reason specifically you're wanting to feed her in a separate tub? It really isn't neccesary for ball pythons, and in many cases can be detrimental to their feeding response. It also puts you in the place of handling a python in "food" mode, which can increase risk of getting tagged.
Anywho, if you're determined to feed outside of the enclosure, the bathtub should be alright for a single feeding (if she'll eat). As long as you watch her like a hawk. If she doesn't strike or seem interested quickly, don't leave or back off "to give her privacy" in the tub. She will find a way out, and you will be posting a new thread about how to find a lost bp. Also, make sure to block the drain hole. Much better to wait, and get a proper tub for her to eat in where escape is not an option, than to give her privacy and lose your python. (again, if she strikes or seems interested in the food quickly, awesome. If she doesn't and is more concerned with finding a way out, just wait and get the better tub)
In all honesty though, your best bet is to feed her in her own enclosure for the best feeding response. Cage aggression is a myth (in relation to feeding), and unless you just rubbed rat all over your hands and went to pick her up, you're not going to get a feeding tag from a python that is well fed. Defensive tags are a whole other ball game (ha) though.![]()