I just read this article on the Huffington Post website about a woman with two vaginas and two uteruses, an extremely rare condition known as uterus didelphys.
The condition usually isn’t discovered until puberty, when the girl starts having what I can only imagine are the worst periods of all time. However, there have been a couple of cases reported where the condition was discovered in young girls (one 5 months old, the other 4 years).
Pregnancy with uterus didelphys can be a problem if pregnancy occurs in both wombs, but there have been success stories. This article describes a woman who gave birth to twins, one from each uterus. And this case report tells the story of a woman who had twins in one uterus and a single fetus in the other–and all three were born via C-section without complications!

Cool! But I cannot even imagine the anatomy of two vaginas, wouldn’t that be confusing/obvious?
From what I’ve read in the different case studies, the two vaginas (and cervixes) can actually be hard to see even with a normal pap smear exam, and before puberty it’s pretty difficult to see it even with an ultrasound. So, I guess they branch off a bit further up than you’re thinking. But, yeah, there are a lot of way-too-personal questions I would want to ask someone if I found out they had this.