Has anyone found a drug or intervention for a dementia patient who is constantly "mean"?

At 95, most people can't handle medications well, particularly psychotropic medicines. On one hand, their brain is very sensitive and delicate and many times it overreacts. On the other hand, the liver and kidneys that metabolize and excrete the drugs are slow and allow medicines to pile up dangerously. Many doctors are reluctant to freely medicate old people. SSRI's are antidepressants that also have an anti-anxiety effect. They are much safer than tranquilizers, sedatives and antipsychotics. As I have mentioned in other occasions, antipsychotics tend to increase mortality in the elder population. Mainly by cerebro-vascular accidents. A younger aggressive and mean patient would have been treated without hesitation with sedatives or antipsychotics. However, a 95 year-old it is a different story. She could die from heavy medication. Sometimes, a small dose of a benzodiazepine like Ativan or Xanax could bring some relief. Valproic acid or Depakote can also be used for aggression, but it requires a normal liver to metabolize it safely. Most people over 90 have poorly functioning livers and kidneys. So, there are many limitations for safely medicating very old people. Social, environmental manipulations or counseling have limited results because of patient's inability to communicate and disconnection with the environment. Aggressive and violent old people with dementia don't live very long. A sudden cardiovascular event can kill them at any time.

She’s 95, has dementia, and sleeps fairly well?

”Mean” you and others who love her may be better overlooked than more medicating.

Take her as she is day to day.

Well, once again I am going to say that only your Mother's MD knows your Mother. Only her medical caregivers know her history, what she is taking, when and for how long and did it ever work or never work and so on. Patients are individuals with individual reactions to things; their own caregivers and MDs know them and whatever WE think is simply guesswork.
You are correct in that the medications MIGHT be causing this, or contributing. And once again, aging is not a whole lot of fun. I am 80. The world begins to change around you. The new gadgetry and the new ways of doing everything are a mystery. Your mind isn't so quick. If the knees don't hurt today well then the backs do.And starting at the head there's the hearing, the eyes, the everything. One gets tired. One gets anxious. One worries more. One begins to wonder what's going to give out next. One either tries to HIDE all this from family for the family's own good or one lays the burden of all that luggage right at the family's collective feed. That's personality. But everyone suffers. One at a time things are taken from you from balance to mobilitiy,from continence to senses, and finally the brain and the very essence of who you are.
So what's there to be real happy about?
All that can lead to depression and contrary to what most folks believe about depression (that it is manifested by saddness and withdrawal) more often than not depression manifests as anger.
I would say that you are dealing with a lot of guesswork here from others, and the more opinions you get the more confusion you may feel.
I would start with talking to Mom. Tell her what you are hearing. Tell her gently and without anger, but with care and concern. Ask her if there is any way you can help.
Next step is the medical check in to weigh all of this.
You will find that often enough there is no certain or easy answer and I sure do wish you good luck.

Dementia damages permanently the neurons in the brain. The main symptoms will correlate with the areas of the brain that are the most damaged. Frequently, the fronto-temporal lobes are affected. That area is responsible for maintaining proper social behavior and anger self-control. This explains why she constantly angry and mean. Unfortunately this is permanent and incurable. Heavy sedation could be used if she become agitated or physically abusive. Citalopram and SSRI's are antidepressant and anti-anxiety pills.

Who is prescribing her antidepressant??

Have you talked to them about her behavior? There may be a better drug for her.

If she isn't being seen by a geriatric psychiatrist, I would strongly urge it. The right meds made all the difference in the world with my mom.