My cat won't stop crying!

Is she an older cat?
I read recently about increasing cases of dementia in older cats, and one of the symptoms is more vocalization. A change in food could be a trigger as memory problems are a big part of it and the cat being scared by unfamiliar things.
If she has also started showing signs of things like restlessness - walking into a room walking around and around like she doesn't know it, and other behaviour changes it might be worth asking your vet about it. It is new for many vets as well but there are resources for vets to find out about it.