Um...the publishing house is purchasing publishing rights to four specific written works of hers, said purchase may or may not include foreign language rights, ebooks, etc, that's part of negotiation and its also what an agent is for. I'm quite sure that at this point she has very competent representation. Additionally, the publishers is buying /these/ works. Not other works that she may produce. She could easily write a book to self-publish in between each of those four books she's contracted for, as long as she doesn't fail to live up to her end of the contract.