Hmmm...
Tread very carefully. I take it this is a non-fiction book proposal you're working on? (Nowhere in her credits does it suggest she would work with fiction, so I hope you're not considering her if this is the case)
If it's non-fiction, then you can get an agent or publishing deal with a strong proposal and a few sample chapters, so I'm not sure how helpful this woman would be. If you're not the strongest writer in the world, but you have a great idea, great research, and other assets, then I wouldn't be _completely_ opposed to working with a professional editor, I would just strongly discourage it.
In any event, you'd be agreeing to pay a person to do what is essentially your job, with zero guarantee of remuneration afterwards. If she's such a great writer, then why isn't she writing? And if you want to be a writer, why would you pay someone else to do your job for you? If your work is in such poor shape that you need to pay someone else just to get an agent to look at it, then how do you imagine you're going to get published? And then isn't the agent looking at her work, not yours?
Why not find a beta reader on this forum? There are people out there who will swap manuscripts with you free of charge, who have just as many, if not more credits, than this woman. If you're willing to do a little critiquing and reading of someone else's work (which can only make you better as a writer) then you'll find critical partners who can help you a lot. For free.
Short answer: if this is a great non-fiction book proposal, maybe just a tiny bit, but probably not. Anything else: no way.
