Pet Rat Vaginal Polyp??

Question
I recently had to take one of my rats an emergency visit to the vets, she is fine now but the vet wasn't entirely sure what it's was and I couldn't seemed to find anything that matched her problem online, usually somebody somewhere has been through the same thing and I would like an idea if this is likely to be the start of an ongoing problem or she is likely cured.

I have four rats and I had let them out but she did not appear,I went to find her and she was in her bed, the paper was covered in blood and she had what looked like at first site a piece of slightly squishy  bloody poo sticking to her but on closer examination it turned out to be coming out her vagina and was obviously causing her a lot of discomfort. She had been out as normal the previous evening, and I am pretty sure I would have spotted anything untoward down there as she is pretty keen on a good tummy tickle, so am fairly confident there was no sign of blood or anything sticking out then. I called the vet and his first though was a prolapse and suggested that the sooner is was sorted the better, so I met him at the surgery. When he examined her he could see straight away that it wasn't a prolapse but he wasn't entirely sure what is was, he consulted some books but couldn't come up with anything (I can't seems to track down anything online either). The lump hanging out of her was probably between 1-1.5cm long and about .5cm wide and was bleeding fairly badly but as it was attached by a thin stalk the vet was confident he could easily remove it. Which he did there and then, I barely had to wait 10 mins and the op was over, a total of 45mins from phoning the emergency number to settling her back in her cage after her mini op. By bed time she was basically back to her usual self and the following night she was romping about as normal, delighted to be back in with the rest.

The only thing that seems to fit what she had is a vaginal polyp but how did it suddenly end up on the outside of her? Or do you have another idea of what it may have been.

Answer
I am surprised it was prolapsed. Without seeing it myself its really hard to say what it could be and if it was a polyp or not. Did the vet send it out to a lab for verification? I would love to know what it was myself. Did the vet mention if it was possibly a miscarriage?