Just to check, you aren't leaving live prey in overnight...correct?

Personally I go with the "tough love" approach. No mice, no smell of mice in the snake room. As long as we're talking about a good sized, healthy snake I just skip a couple of feedings so they are good and hungry then offer the new prey type. Sometimes it takes a few weeks but most switch over for me.

Just a couple of things to remember though. Make sure the new prey (rat) isn't significantly bigger than the old mouse prey. If you aren't sure, err on the side of caution and go smaller. You can always work up in rat size once she's comfortable with eating rats. Some will never switch. While not all ball pythons are prey specific hunters, some are. I have some here that would rather starve then not get what they like to eat. Most of mine are not that picky but a few are and I just have to deal with that fact of life.

There are a number of tricks you can use - pre-scenting, rubbing the rat with used mouse bedding (scent transfer), putting a little pile of used mouse bedding in the corner of the snake's enclosure before the rat goes in (another type of scent confusion I guess you'd call it). I'm sure a few members will weigh in here with the methods they've used successfully.