How do I handle delusions and paranoia from dementia mom (90)?

With medication. Usually a geriatric psychiatrist is a good person to have on your "team".

There are good meds that will help with the delusions and paranoia. It may take some experimenting to find what will work best for her.

Just as important, is how YOU deal with these problems. Do not try to correct her. This will only increase her agitation. Find ways to distract/redirect her with things she enjoys. A TV show? Music? Her favorite treat? An activity of some sort to get her brain in pleasant places? I never used old photographs as that would agitate my mom even more. Why? She would start to worry about those people and wondering if they were alright. Many time her parents, who had died years ago.