Im not sure, but maybe its just her getting ready to lay and not actually a prolapse?
When i first bred my female a few nights before she lay she was running around frantically and her vent appeared to be pulsing and appeared to actually be "comming out". Its hard to explain, but i think if she had not been contracting and had just been sitting there it would have definately looked like a prolapse. Maybe that is what you are seeing?
Other than that, until you can get to the vet, keep it clean and hydrated. Sugar water soaks or milksoaked paper towel wraps work well to keep the area hydrated. if she is on a sand or sand like substrate keep her on paper towels (of course, except for her nest box) until you can get to the vet.
Good luck!!
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0.1 Bearded dragon
0.1 mexican Black kingsnake
1.1 Leopard Gecko's
0.0.1 Tokay Gecko
1.0 Blue Tongue Skink
0.0.1 Reverse Okeetee Corn
0.1 Anerythristic Corn
0.0.1 Red Tegu
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4.1 Cats