There is a disease that is related to Parkinsons that is called Lewy Body Disease. The symptoms are very similar, but hallucinations are much more frequent and pronounced and sadly it does progress to frank dementia. My mother had this. She was initially diagnosed with PD, but it gradually became clear what the real nature of the problem was. I do not say this to worry you - iit is best to be clear about what the situation is. Knowledge is power and all that. My poor mum kept seeing babies on the sofa and was always worried that we might sit on them! Her hallucinations were never frightening ones and she did not seem the least disturbed by them.
The Parkinsons UK website will help you with this as well.
My OH has lots of help - speech, nutrition, physio - as well as his drug regime (which is very complicated as he has a heart problem as well). The Parkinsons nurse can keep tabs on symptoms as they develop and ensure that the proper treatment starts.
Another thing to think about is this hot weather - if your sister is at all dehydrated this will have an impact on the drugs and their concentration and effects.
My OH is on several drugs and the consultant needs to be kept up to speed on any problems so that interactions can be considered. Everyone responds differently.
Mattress causing back pain - or is it me getting old?? Advice please.