This is probably a terrible thing to say, but if she was truly anonymous - if she approaches a new publisher as if she was a complete stranger - would she be published? Particularly in a different genre? Almost all new writers are rejected. I like the Potter series - I've read them all. My greatest triumph was to correctly predicting the big reveal at the end of book 7 when everyone said I was crazy. But I have to admit that she started to sprawl after book 3.
Books 1 to 3 were tightly written, but then she became bigger than her publisher. They did not dare to edit her beyond fixing typos. The books tripled in length, including every little detail. Which is fantastic for a Potter fan, but less exciting for the casual reader.
I wonder, if she produces a huge, sprawling book in a genre she does not know, and presents it in an anonymous brown paper wrapper to a publisher, would it be accepted? Publishers get thousands of manuscripts, and I am sure some of them are excellent, yet nit everything can be published. Plenty of famous authors were rejected many times. There was even an experiment a few years back when Jane Austen books were anonymously sent to publishers, as if they were by a new author, and many were rejected.
The cynic in me thinks that her publisher will know her name, and will rely on that fact. They know that, regardless of the quality of the work (which of course may be excellent, but all publishers and fans say their books are excellent), sooner or later her real identity WILL leak out and then high sales are automatic. the real test is whether the new books sell more or fewer copies with each new release.