As the boy's Mother I believe you have every right to see that will. Even with nothing there of benifit. I understand not wanting to be confrontational,especially in a sensitive situation like yours, but it may not be a way around it unless your willing to get the courts involved, which I believe you should if it came down to it. Either way, I don't think you should let this go at all and I'm hoping you're able to get through to her with a serious talk maybe. If that's of no use, You should your lawyer.
My regards-