More than two regurges (in a row) are very concerning. Give her at least two weeks with no food so her gut flora can regrow, then offer her a much smaller meal, like a hopper. If you want to order some nutribac that can help too. Just dip the mouse in it before feeding.
All that being said, she is 18, a pretty old age for a corn snake, so there might be something age-related going wrong inside her. A reptile vet might be able to give you some more insight.
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