Judith - do you know whether your mum has developed dementia due to her Parkinsons? There is a special type of dementia, lewy body, which is typical in Parkinsons disease. This causes hallucinations and delusions. I'm not sure whether this has been mentioned to you or whether you have had any help from the Parkinsons Society? I only know about this because a neighbour I was very close too developed lewy body a couple of years after being diagnosed with Parkinsons.
Taz x