Crack open tub just enough to introduce prey, allow her to strike and constrict, and while she's pre-occupied, gently pull the tub out a little further to spot clean and change water? Might help if you have a spare water dish to just swap it out. I have a couple snakes that actually don't mind me carefully lifting them out of a dirty tub and into a spare clean one while they're "killing" their ratsicles, that way everything is fresh and clean with me only having had to disturb them for the three seconds it takes to move them, then I can just slide the new clean tub into their spot in the rack like nothing ever happened.