My mother is being really difficult in her nursing home. Any advice?

I think you answered your own question in your very last sentence when you said that perhaps just kind words and thanks to the staff along with some occasional goodies is all you can do. That can go a long way.
I'm sorry you have such a hateful mom, but that is on her not you. When she starts showing her ass when you visit, you just get up and walk out the door and tell her that you will come back another day when she is in a better mood. And you keep doing that over and over, until perhaps she gets it.
And if she doesn't it just means that you don't have to spend as much time with her as you probably have in the past.
So at least it's a win win for you.

Go with the kind words, thanks and snacks for tea break. In an effort to make the staff's work a little easier: I added an assortment of air fresheners and a mini portable fan for my mom's tiny bathroom. Be sure to "report" all the good things that normally go unnoticed.

As a retired NH clinical staff member we all knew nasty residents. We felt bad for the families. We were less stressed by these older gals {seldom were the men as disagreeable}…I suggest you remember it is NOT your job to make her happy..you provide a safe place. It is her job to find a way to navigate in the world..even in the NH world. Do short visits..leave when she is mean. If she wants visits she will learn to play nice!!

The staff should be used to, and trained, to handle this, so it's their problem.

If she's so unpleasant during phone calls and visits, then she doesn't deserve the time you take to do so, so stop visiting and accepting her calls or calling her if she acts like a baby.

If she's always been this way, she won't change now. So you've pretty much done all you can. I'd avoid her as much as possible, she sounds like an energy vampire.

Send thank you note to the staff and maybe a snack - tell them you know mom is difficult and you appreciate their hard work.

Get mom to see a geriatric psychiatrist. She might benefit from counselling and/or medication.

My sisters MIL was a self absorbed person her whole life. When she experienced dementia and inability to self care, she lived with them. My sister and her husband took her to the doctor and explained the situation. The foul language, lies, confabulations etc. were minimized with what my sis called her Happy Pill. I don’t know what it was, but it decreased the anxiousness and managed to soothe the old lady. Unfortunately, my sister wasn’t great about keeping a supply so the poor woman would run out and exhibit the behaviors that the med was modifying.
Bottom line: ask the medical staff for a recommendation. My own mom was always sweet and her behaviors declined to paranoia and fears/anxiety. The doc prescribed Olanzapine/Zyprexa. 10 mg to start since she was really over the top and then 5 mg. The positive is wonderful and when we tried to wean her off per her doctor (just to see if it was helping) she went back to mean, paranoid, anxious. We will never run out of these meds. The contraindications on the box are sobering, but I researched and read the papers of research and it is worth it for my mom since she is never going to get better and her terrors are abated with that little pill.

As a hospital staff, I got training. You have to separate the personality from the disease and sometimes the gap is short. I have seen many mean people in my career. They tended to isolate themselves, and the constant callers would just keep calling. Let the staff deal with it. As for visits, make them shorter and call her on her abuse that the next thing she says will mean that you are unwelcome.

Definitely side with the staff. When in doubt, side with the staff. You and the staff need to look like you are in complete agreement with her care.

Unless you know the staff can make bad life threatening decisions, in which case, you need to move your Mom out of the facility.

...and just to be fair, if the story your Mom is telling is plausible, side with the staff ("Oh I'm sure there is a reason for that"), then start asking probing questions to your Mom to see if the story really is the whole story. If there is enough evidence to wonder, ask the staff for their version.

Just in case something really happens to your Mom, you don't want to completely shut her down. You do want to know if the facility is not performing up to your expectations, and your Mom is the person who would alert you.

Funny story: My Mom is in MC. For successive days, my Mom said that the staff did not give her a bath. Her hair looked like it had not gotten washed and her odor was "different." so the story was plausible. When I talked to the staff, they said that my Mom was refusing to bathe, saying that she didn't need it or thinking she had already taken one. I went back to my Mom and I said, "I heard you are refusing to take a bath." She said "they try to give me a bath 2 times in the same day and I tell them I don't need it." I told my Mom, "If they ask you to take a bath, you take that bath. I don't care whether you thought you already had one or not, just take the damn bath." She argued, I repeated myself. That night, when the caregiver came to give her a bath, she said "I know I already had a bath today. But, I better take the second bath or my daughter is going to be mad at me." We all got a good laugh. Success!

I don't have an answer for you. My mom was a nightmare in her facilities..yes plural! She eventually managed to escape to her own apartment years ago. She now lives in low income housing with home health. I can image majority of patients in a nursing home are negative. It's not a great place to be. You need to assume the staff are professionals and can regulate themselves majority of the time to handle the behaviors in a professional and appropriate way. There are methods to handle grouchy and mean residents. Some staff take it way too personally. Some know exactly what to say to de-escalate.

I’d suggest that you minimise visits, and take with you a packet of nice sweets. When mother is rude to staff when you are there, give a sweetie to the staff member and say “Thank you for putting up with it”. Leave when you get told you are the enemy too. Tell mother that if she thinks she employs the staff and pays their wages, she will need to go for a sanity test.

It sounds as though you have let your mother get away with this for far too long. But it's never too late to change.