Chimera was my best guess, which is one of the ways you end up with two-headed snakes. As I mentioned on Skype actually proving that she's a chimera is difficult, would require genetic tests on samples from the body and each of the odd growths. There are other explanations, it's possible it was caused by a failure in the mechanism that controls growth as an embryo. I'm sure there could be other causes as well. It would be worth taking regular photos of the defect so that you can pick up any changes, I'd be interested to know whether there is any growth of the extra tails, or whether they become relatively smaller as she grows.
Whatever the cause, I'm sure that most of the time this sort of defect would lead to a stillborn.

She's a beautiful snake Steve.