Even if this were an editor at a publishing house, at the end of the day, the decision would still be yours. Of course, in that case, you might risk the editor not publishing your novel, but that is not the situation here. You have paid for an edit, and she has given her thoughts, and you don't believe that they work for your ms. You have no obligation to edit according to her thoughts--you paid her, so she still got rewarded for her work--and the only risk is that she knows something about the market that you're missing that could potentially keep your book from selling, but it could totally be that her own preferences are getting in the way of helping your book be the best it can be.
I know you're reluctant to come across as argumentative, but I think you should talk to her and tell her where you guys are disconnecting on the purpose of the book. It is possible that she felt she was so right about changing it to YA that she didn't bother making notes under the assumption that you wouldn't but that she has plenty of thoughts on it if you keep it adult. It's also possible that she has reasons for her suggestions that you just don't see, and that she can explain them to you in a way that suddenly makes sense.
I know you're reluctant to come across as argumentative, but I think you should talk to her and tell her where you guys are disconnecting on the purpose of the book. It is possible that she felt she was so right about changing it to YA that she didn't bother making notes under the assumption that you wouldn't but that she has plenty of thoughts on it if you keep it adult. It's also possible that she has reasons for her suggestions that you just don't see, and that she can explain them to you in a way that suddenly makes sense.