I rescued a couple balls about a year ago, both about 5 years as well. The female was VERY dehydrated. I gave her a few good soaks and eventually she would drink while in the bath tub. Many ball pythons really hate the water but it's all about the individual snake... You could try using a tub with a locking lid if you're worried about being tagged.

Also, I've heard of people soaking them in powerade because the snakes can soak the electrolytes up through their skin. I've never done this though. If they're taking food you could soak the prey in water to give them a little extra hydration.

If you really want to look in her mouth you could take a wire coat hanger and cut one of the shoulders off. Hold the snake behind the head and use it to open her mouth (STERILIZE). Mine had mouth rot as well as a RI, so this was the method the vet gave us to administer the pills and also to clean her mouth.