How old is your Pap and how long has this been going on? Has it always been that way or just lately? Is she spay? The most common cause for swelling of the vulva is a female being in heat. Has a Vet checked her? Is she licking the area? This could be a fold problem in the vulva area that might require surgery. This could be a chronic infection that would need extra care cleaning the area and antibiotics and/or topical ointments. It could be an allergy to something she is coming into contact with. Is there any discharge?
Has this been the case in all the time you have had her? Has she been spayed, or not?
A very swollen and often redddened vulva usually happens when a female is on heat, usually for a few days right in the middle (the second week) then it returns to normal shape. But that would only be the case, of course, if she hadn't been spayed.
It is vaguely possible that she is just that shape naturally...? But probably you would have noticed it all her life if that were the case.
Is she showing any signs that this is irritated? Like licking at herself, or showing any discomfort? If she HAS been spayed, and this looks red raw and irritated, then my suspicion would be that she has a possible urinary infection. If so, that's easily and quite cheaply treated.
I think you maybe ought to get her checked out...if you take her to the vet, take a urine sample with you.