My mother died on April 28, 2012.
About a week after her death, I believe it was on May 7, we heard a noise and I looked out the window. It was dark outside, and I saw light coming out from the garage downstairs. So, I knew the garage door was opening. My husband and I went downstairs and observed that the garage door was opening and closing on its own. It would sometimes open or close only halfway. Very odd. I more or less dismissed this as some electrical malfunction. My husband felt like it was my mother sending a message. It never happened again.
My sister told me she astroplaned the night our mother died. I didn't take it seriously, and in fact forgot all about it. My husband told me I mentioned it to him, so definitely she told me this at some point. It's a different subject, but all she says she remembers is falling out of the ceiling into her bed sometime in the morning.
Fast forward to October 2019.
On October 18, my sister called and we talked about our mother. The next day, around the same time, about 7pm, both smoke alarms went off simultaneously, and there was no smoke. I pushed the button underneath the one in the foyer several times to quieten it, but it had no effect. Both smoke alarms stopped about a minute after they started. Very soon afterwards, my husband said it was my mother, and that it was because we were talking about her the day before. I recalled the garage door situation, and felt it was plausible.
My mother's birthday is October 22.
My sister lives in rural Indiana. Yesterday, October 24, she called. We talked about my husband's illness. Then she told me her best friend committed suicide. To change the subject, I told her about the smoke alarms.
A few seconds went by and my sister told me she had goosebumps from what I just told her. She said that she was cooking a pizza on our mother's birthday. There was no smoke in the house, and two of her smoke alarms went off. In the same fashion, they both stopped at the same time.
I believe my mother is trying to communicate.
Perhaps you should ask your sister to give you a full account of what she remembered? If you already know? It would be a nice add on to this story.