Hi @gepetto.
One of the best things I got early in this process was a one-pager from the Alzheimer's Association with communication rules. This site will not let me post the URL for something like that but you can google Alzheimer's Association Compassionate Communication San Diego. They have a good one.

Many people who are trying to be nice think that the polite and caring thing to do is to ask the person questions. That creates stress, of course. So, I tell people to talk at my husband , i.e., tell stories, describe recent activities, talk about shared experiences (without ever asking if he remembers those things).

I also ask them to please look at him as well as at others in the group, so he has signals that he is being included.

Shaking hands or just a pat on the arm or on the shoulder can also create a warm feeling of connection.

Important: Remind them that the level of verbal skills does not reflect what she can understand.

Encourage your relatives to really let her know that they are glad to see her, have missed her, appreciate her. The more specific they can be about things that they have appreciated about her the better. Hearing those things will evoke emotions that can be more enduring than conversations alone.

It is wonderful that the family will be together. Have someone take photos! Those may be helpful as the memory of the event fades in her mind.