I know this is such a tough situation but I agree that when you're in your own territory, your own home, you should expect and demand respect.
I tried the "killing her with kindness" routine. Two months ago when my sister who has been shunning me for over a year called to come to the hospital to see my newborn son, I allowed it. But on the condition that she has to come upstairs and wheel me down to NICU. Well, she completely ignored that request and tried to get into NICU without me. The nurses had been tipped off and sent her upstairs to get the baby's mother. HELLO!!!! Anyway, long story short, we talked (she had to because I wouldn't cooperate with her shunning while she was wheeling me down). She was polite and civil, although it was forced. So I'm thinking, "Hey we made some headway..."
NOT! The next time I saw her she shunned me worse than before. She tried to say hello to my husband though. Guess what! He looked her straight in the eye and turned his face and walked away. To me that was such a sign of loyalty and respect on the part of my husband. He said, "If she shuns you, I'll shun her." And guess what! My 13 year old daughter chimed in and said she's going to shun her too. And there's nothing I can do about it. Part of me feels supported and happy that they're backing me up. The other part of me feels sorry for my sister and I want to hug her since I know how much it hurts to be shunned by someone you love. It's a no win situation. If you're nice, you get screwed. If you're mean you get screwed.
The thing is that you can't "kill them with kindness" because then you're cooperating with the Watchtower rules. You can't ignore the fact that they're disrespecting you. I think that maybe you should have said, "Hi mom. How are you doing?" And then when she proceeded to be rude, "Listen mom, I respect your right to shun me. But when you're in my home, you are going to have to respect me, otherwise you'll have to see your daughter somewhere else. It's YOUR DECISION!" Then let her walk out on her own. Let them be the bad guys. Besides, isn't that what the Watchtower says, "It's the individual's personal decision to shun family members .... it's the individual's personal decision to refuse blood and die .... it's the individual's decision not to go to college ...." Well hey, IT'S THE INDIVIDUAL'S DECISION TO BE KICKED OUT OF MY HOUSE!