My Mom's falling a lot. She has dementia, is this a stage of this?

You didn't state what kind of dementia your mother has. I can only tell you from my experience with my grandmother and my mother who both had Alzheimer's. They started falling when they forgot they were walking. My mother was put in a wheelchair to prevent further falls and forgot she ever could walk and never tried to get up.

It could be part of dementia and she should see the MD ASAP

I'm not a medical person so my answer is based on experience and my own personal research.

One of the Area Agency on Aging Expos I've attended included a presentation by a neurologist who addressed falling issues. He addressed 3 primary factors of falling: sight, hearing, and unfortunately I've forgotten the third although I think it's balance.

Assess your mother's health - does she need hearing aids? Are her glasses current? Does she have cataracts? Does she use a walker? Does she have difficulty walking?

Has she actually been diagnosed with dementia, and if so, what type of dementia? Have you researched that type of dementia to determine if falling is a characteristic or side effect?

Beyond this, there are the medical issues, such as whether she's getting enough nutrition or if she's not and feels weak, and/or dizzy. Is she able to participate in therapy to strengthen her legs? Have you discussed this with any of her doctors?

If she has dementia, her sense of life around her has changed, and that could be a contributing factor, but be sure to address other issues mentioned above as well.