I want to tell you about our family. My elderly mother is the only one who is still a JW. I have a niece who is gay and she came out to the family many years ago............she is in her 30's now. We were still JW's then, but we accepted her because we love her. We rarely saw her in those days, but her being a gay woman didn't change our love for her. She had been raised as a JW until she was about 14. At that time, her mother died, and my brother, her father, went through a terrible time, eventually stopping being a JW.
My mother, her grandmother, accepts her and her partner, no questions asked. It is amazing to all of us that she responded the way she did, but she loves her grand daughter.
Don't assume your mother will react badly. I am sure she will be shocked, and probably hurt and disappointed, but she loves you. Even if she had a bad initial reaction, she will come around. Don't underestimate a mother's love for her child.