Issues with not wanting to have children!

Jessica
So, my SO and I have been together for 4 years now. And his mother constantly mentions that once I'm done university that I'm going to have her grandchildren. And both me and my boyfriend have told her we don't want kids, and if we decide to we are going to adopt. She says that it has to be "our" baby. The other problem is that I have type 1 diabetes and it's possible I won't even be able to have children without complications, which we have also told her, and she still says that I'm going to birth her grandchildren.. 
Has anyone else had a similar situation, and how have they delt with it? My SO and I are totally on the same page with the whole kid thing. And my parents are also supportive and know I don't want kids and are also totally fine with the idea of adoption. I know I shouldn't really care what she has to say about this, but I feel like if I don't have kids that I'll be disappointing her and then she won't want me with her son..