Can an assisted living facility make a resident stay in their room for all meals and have no contact with other residents for being rude?

The military past is completely irrelevant. This is civilian life, not the Marines, and the other residents aren't grunts.

If she truly can't control her behavior, then she probably needs to be in memory care, not assisted living. They have a bit more tolerance for people's quirks, but nevertheless she doesn't get to run roughshod over other residents regardless of where she lives.

This is something for the resident, her family, and the administration to handle.

I'm pretty sure the military would have disciplined an obnoxious soldier who couldn't/wouldn't remain civil at meals, maybe you should point that out to her.

Read the facility policies. If she is disturbing others then I would think they would have to handle her meals differently. It is not reasonable to expect all the other residents to tolerate rude, obnoxious behavior during meals. Maybe they could seat her away from others but that doesn't mean she will stay there.

Think about how unpleasant it is when you are eating at a restaurant and there is a child experiencing some sort of tantrum and how disturbing that is. This is no different with the exception that elderly in facilities do not have a high tolerance for bad behavior.

In an ALF the facility itself makes the rules. Period. And they make those rules for the greater populace at large.
My brother, in his own ALF used to laugh with me that it was a bit like being in a commune in the 60s. There would have to be community meetings to settle the squabbles. Myra wants the shades in the common room up for the natural light so she can draw. Doreen wants them down because the light disturbs her eyesight. That sort of thing. And yes, there would be the occasional disagreement.
There were in the common room tables which were game tables and mealtime tables and people ate together at a table. Sometimes one or another didn't like a table mate and moved to another table.
However, if Mom can't get along at ALL the tables, you can see that is a problem. And yes, they can ask her to eat on her own that being the case. And yes, if she is not cooperative because she is exhibiting dementia she can be asked to move to a higher level of care, memory care. And yes, in fact she can be asked to move out of the facility altogether.
At my brother's ALF we were given a huge packet of admission papers. Among them was the portion dedicated to the reasons we might ask you to leave the facility.
So this would be the norm in most facilities. I don't know if your Mom can "understand the rules" and react accordingly (in the Military that is a requirement), or if she can no longer hold her peace no matter the requirements. Discuss it with her. Don't criticize but do explain, gently, the consequences, and who is in charge. Again, being in the Military she will understand that.
As my bro used to say "I am pretty private and don't necessarily like living in a "communal setting" but you know, it's like the army; I make the best of it."
I am afraid Mom is going to have to give that a try.

If the resident is former military she should know that there are consequences when rules and orders are not followed.
They have no right to stick her in memory care if she has not been diagnosed with dementia. Memory care is for people with dementia.
People are rude and unpleasant every day. They don't get sent to memory care.
I would be on the side of the AL with them prohibiting her from taking meals in the dining room if she's acting up and disturbing the other residents. Why should they have to tolerate her rude nonsense during mealtimes?
And, it's okay if some folks have said you don't talk 'nice'. I don't either. People often mistake plain speech for rudeness or not being nice. Not the same thing.
If this resident doesn't have dementia, she needs somebody to put her in her place and tell her plainly that either she keeps her behavior in check or get used to dining alone three times a day.

I'm in a NH. I hate going to the dining room. I've only been three times. It's loud. The occasional loud repetitive screamer, intrusive people going from table to table. My answer to my problem is I started paying extra to have my meals delivered to my room or sometimes I go out for lunch or dinner. Better than complaining about a problem that probably can't be fixed.

This happened with my grandmother….she turned into a verbal
aggressive elderly person….cursing, shouting etc. she was removed from the dining room from this.
we have to protect all residents.
i can’t imagine one resident upsetting multiple residents….that would be a nightmare to handle

I hope this doesn't come off as sounding rude...Have you really seen the facility staff tell this particular person to stay in their room or away from other residents?

My mom has a tendency to tell stories, and that sounds like a story she has told me often about staff. It seems like (in mom's eyes/mind), that staff is always changing the rules for her.

I've asked staff about some of the stories mom has told me, and that is what they are...stories.

Does the person suffer from Dementia? If so they have lost their filter and cannot be reasoned with. So, to make meals pleasant for the majority, they have felt it better the person eats in their room. Its not a punishment in the sense of the word.

If the person does not suffer from Dementia then not sure if they can keep them from eating in the dining room. They are paying to live there and it their residence. I would think, though, that the person has been asked to tone it down and when they did not do it, they were asked to eat in their room. Really, if you choose to live with others you need to know how to communicate with them.

It is called consequences for undesirable behavior. So in a way, yes, punishment. But not overly harsh.