How do I do the right thing for Mom - telling/ not telling her the other daughter isn't coming now?

I suggest that you tell your sister that you will not be the conduit for communication. Sis can pick up the phone, call Mom, and tell her she's not coming.

I would have your mother call her.  The sister needs to tell her this on her own.  It is wrong for her to expect you to be the bearer of this news.

I would bow out of that, let your sister tell her, it is her call, not yours. So sorry about your mother.

My prayers to you and your family during this tough transition--My father is currently in hospice and I don't know if he will last around for the holidays. Hugs.

My sister has a good analogy - every relationship is a circle with each person having their side of the circle and needing to stay on their side.

In this situation, this is not your circle. But, what a difficult position you are in if your mom is asking for her!

If your mom is able to talk, can you call your sister for her? You might be accused of blindsiding your sis if she doesn't know the call is coming but putting you in this terrible position isn't right or your responsibility.

Wishing you peace through this journey.

You’re doing enough, more than enough, you’re being a great caregiver. Please don’t take this on also. This is between your siblings and mom, let it be on them

Your sister was informed, and now it is up to her to decide. Do not waste one minute worrying about what she is going to do. Spend your energy and time on your mother. She knows, and now it is up to her to visit, or call. I would not tell your mother, let your sister do it!!

**Update to all who answered.
Thank you so much for giving advice.
It was nice to have the support.

Unfortunately, my Mom passed on Monday.
She asked me Saturday when will she be getting here. I told her I had no definite answer yet. And then by the evening she had started slipping away.

I'm so grateful I could hold my Mom and be here for her. It was hard, but man I wish everyone had this when they pass.

Call your sister and hand your mother the phone and tell her who it is. Walk out of the room for privacy and let it go. We each have to make choices and live with it. Mom lives with me and 4 sisters close by and we each have a separate relationship with her. I won't have any regrets in the end but can't imagine how one of my sisters could live with herself. Not only are none of 5 of us on the same page, we're not even in the same book! I think of what will they remember about me when I die and I hope they remember kindness, unconditional love, laughter and forgiveness for treating mom the way they have. I would try and leave the goodbyes (or not) to the two of them. Very sorry for your situation.

I would ask your sister to call mom directly or you call her and put your mom on the phone. Your mom could also call her. She could leave your sister a voicemail if she doesn’t answer.

Why should you have to deliver the message to mom? Not fair to you. Are her reasons valid for not being there?