Give them an incredulous look and say, "Really? I'm here to be with my mom. Now is not the time. In fact, there is no time that this is appropriate. In spite of all promises to the contrary, my mom grew old and is dying. You are too. Resign yourself to it."
I'm glad you are with her and loving her to the end. JWs do a lot for nothing all their lives. Having family is all anyone really wants when it all comes down to it. She has that. I'm happy for her.