To be honest, it shouldn't cost much at all to simply take her in and get her looked at.
Our vet charges $15.00 for a full exam including palpations, anal gland exam, tear ducts, oral check, hip check, stool check, ear exam, (the basics).
I would at least take her in so the vet can look at it.
It may be something very minor, and it could be something life-threatening.
Fact is, you won't know unless you take her in.
Like I said, it shouldn't cost much. Most vets will have a rough idea of what it is by viewing it, since they deal with pets on a daily basis; that's their life.
You'll feel a lot more at ease knowing what it is, too.
I pray she will be just fine, and that it is something minor and easy to heal.