A Corn's ideal maximum temperature is below human body temperature, so yes, it could have felt scalding to her. "Lukewarm" is subjective - you're best to check the water temp with a thermometer if in doubt.
Some Corns really don't like being bathed and get very stressed when you try it. With these, it outweighs any benefits, so just don't bother.
You don't actually NEED to bath Corn Snakes at all. Some folks do it to give exercise and improve muscle tone, and in some cases it can cure constipation (although I'm in two minds as to whether it's just the stress that loosens the bowels!). However, I've never bathed any of mine and they're all perfectly healthy.
If you're worried about a Corn being dirty (e.g. after sliding through a nice fresh pile of poop), then the best way to clean them is to make an old towel damp and let the snake run through it as you hold it. Again, no need for bathing.