Hello Langdon,
You must be feeding Molly very well, making her come into having milk!! Only joking
Some goats can give milk, before having been in kid, usually happens in summer, when there is a lot of grass to eat. I had a very large, and I mean large, British Sanaan nanny goat. Took her to the billy, but never bred. She got an udder every summer though, and I would milk her. Then the udder shrank in winter, and she gave no milk.
That could be what is happening with Molly, but if you do not milk her, it should dry up, and she will have no milk. I assume the udder is only slightly swollen, not a great big one?
The other possibility, is that where the scab is, could have been a cut or a graze maybe, from browsing and eating bushes and brambles or something. It may have caused an infection in Mollys udder, but I am sure the vet would have noticed if that was the case, so probably not that. Mastitis, usually in summer, when the flies are around,........definitely no flies here yet.
I would keep an eye on her udder, and ring the vet again if there is any growth in size of the udder, or any redness or change in the size or shape, or any discharge from the teats. That could be a definite sign of mastitis .
Hopefully, its just as I said, she is so well looked after, she has started milking!!