Mom is hallucinating, please help?

You may never get rid of this. Does it disturb her? That is the main question.
My brother suffered from Lewy's and was actually diagnosed as probable early Lewy's Dementia. He actually enjoyed most of his hallucinations. Guess what? One was a pool party out the window. He would go on to describe to a T everyone there. A man who had black hair and an Elvis haircut all slicked back, white shorts and a white towel over his shoulder and so on. Another one involved an immigrant woman in the corner of his room, sheltering and crouching protecting a baby on her lap.When he reached to comfort her, poof she was gone. He would describe the hallucinations full out and knew they were not real, but seemed so to him. Often brought on easily with patterns seen in carpets or in marbled walls, busy wallpaper. He delighted in describing how differently his eyes saw the world. He died last May at 85 cause unrelated to his diagnosis. He never wanted to go into the darker world of dementia, and I am relieved he never had to.
This is something, if your Mom is upset about them to discuss with her Doc. Hallucinations are common to some dementias such a Lewy's and to Parkinsons which can have some disturbing paranoid delusions as well.
97yroldmom below suggests the UTI, and if these are sudden onset and new for her that is a REAL possibility, so start with her regular MD.

UTI’s often cause increased dementia symptoms and in the elderly don’t always cause the expected symptoms of frequency of urination or burning. Anytime an elder shows a change in symptoms, it’s worth checking and relatively easy to do. UTIs can be toxic.

Call doc, she could very well have a UTI. Her geriatric specialist a geriatrician.

There are over the counter tests available but you would still need to get her in for a test to get antibiotics.