I've seen funeral customs change a bit in my lifetime.
When I was a child we all went back to the home of the next of kin, and had a meal from all the foods that neighbors had brought since the death. There were usually enough foods brought in that the family didn't have to cook during the previous several days of funeral home calling hours, either.
Nowadays where I live there is usually a luncheon in the church hall after a funeral, or sometimes in a restaurant. When I've been to a restaurant after-event there has always been a set menu. Sometimes there is a meal for only the family, but not always. Generally, it seems to me that people don't go to the after-event unless they are very close to the family, even if a blanket invitation has been given.
It seems like people are having fewer calling hours, too, and there are more funerals in churches than in the funeral homes. Many people now have just a few hours of calling, followed by the funeral.
In your case, Figgie, it sounds like for whatever reason your aunt does not want to spend time with and deal with her late husband's relatives. It's understandable that this makes you feel a bit uncomfortable, because they are grieving too.
I think that a grieving widow should be given a pass for many things. It's unfortunate that she is going to do this, though, because the excluded relatives are likely to be very upset if/when they find out that they have been excluded.
I wonder what aunt will say if they directly ask her about a post graveside event, or actually invite your aunt to something that they have planned.