Should I tell my Mother that my sister, her oldest child, died?

I wouldn't tell her either. My nephew committed suicide when my mom was at about stage 5-6. We did not tell her....just too stressful.

I wouldnt tell her right now. I think its best not to "rock the boat". If your Mom isn't asking about her non-stop or demanding to see her 24/7, I wouldnt bring it up right now. There's no purpose and it would only upset her. The only way I would tell is if she kept asking to talk to her on the phone 24/7.

Things have a timing and if your Mom is stable, doing well, relaxed & settled down, then why rock the boat and tell her. If she starts to go crazy in a few months and keep asking to see her everyday, then you might have to tell her.

I agree, don't bring it up, don't say anything except sis is doing really well.

My heartfelt sympathy to you and your family. You are making a wise decision not to tell your Mom that your sister had passed.

With advanced dementia, if Mom is told, she will grieve... then an hour later she would forget she was told. She would grieve each time told.

Thus any time Mom asks about your sister [sounds like she might not] just say she is busy and will visit next week.