Oh my, this couldn't be stickier, and regardless it is hard seeing a friend and business partner you care for going through this. Given that she has been so quiet on this does indicate that she knows/suspects something.

Given my recent "putting both feet in mouth" incident I've no business giving advice - but I like your idea about putting yourself in a supportive role. Letting her know that you are there/concerned for her does indirectly indicate that you know at least something of what is going on and may make it easier for her to broach the topic and is quite different from simply remaining silent. The professional relationship does make things more complex, but in the end you have to do what you can live with - regardless of how all of this comes out.