I read your story like three different times to make out what you disturbed you recently. I see that they actually gave your mother a seat up front, which she didn't want, however, I think they were trying to accomodate her without giving much thought that she may not have wanted to get split up. At 88, first class is much better and comfortable for her. Sometimes you get boarding passes to your next destination with assigned seat numbers, but when you get to the gate, things change, and they re-issue passes, usually in your favor. I don't think your mom got ignored, if anything, they probably thought that they were doing her a favor. I doubt any of these actions were deliberate, and intentionally done out of malice or neglect. Sounds like you may have gotten just a little bit defensive with your aging mother and travelling with her could have added up alot of stress. I know that feeling.

Once I was travelling from Japan with my wife, and the decision we made was that if we got split, one in first, other in coach, I would take FC because of my size in comparison to her. She is way little and I am way big. So what makes sense? Secondly, I thought we could swap for like during breakfast, but the flight attendant didn't allow it. She said it was because of security issues. This kind of ticked me off a little. Also, I do forms for both of us and when wife walked up to ask me about it up in first class about an hour or two before landing , the flight attendant got a little unglued about it and told her to go back to coach. Flight attendant was doing her job but I was a bit protective of my wife so I had to bite my tounge.
I don't buy that security BS either, I just think old hag didn't want the peasants showing up in first class regardless.
Advice, nobody got hurt, nobody missed any flights, just let it go.