That's so sad. Since you aren't disfellowshipped or disassociated she is actually going counter to the bible by choosing to listen to gossip and shun you without even talking to you, but at this point there is nothing to be gained by calling her on it.
My mom passed away shortly after I left, it was a very difficult time, no one told me she had gone into the hospital, I was only informed when she died. How could that ever be an OK thing to do??
It just shows how evil the Watchtower teachings actually are in practice, that they can tear families apart and cause such heartache and grief. Rather than motivating me to return I was just more determined to have the stupidity stop there, no way was I ever going to shun my children.
I have found meditation to be very helpful with the stress of dealing with JW family.