Mt grandmother suffers from dementia, although earlier medication was given for parkinson's. Can you suggest some medication and advice?

Seek an expert. It sounds like she should see a geriatric psychiatrist or a neurologist specializing in this area for advice.
Dementia. Dementia is often associated with sleep disturbance , behavioral problems, and depression. The rule of thumb with meds is go low and slow targeting all brain receptors after doing a simple genetic test for cyp 450 and test medication response. After that is done an antpsychotic -antdepressant-antiseizure - deplin and B12 but needs to be taylored to patient presentation and stage.
Not the same. Parkinson's usually presents as a tremor in the hands, both dementia and Parkinson's can occur in your grandmother's age, in the same person, so it is possible that she does have both. There are some helpful dementia medications, like Aricept or exelon, (rivastigmine) Namenda that may help her dementia, it depends on the cause. So can be applied as a patch to minimize the possible nausea-talk with her dr.
Parkinson's ? Actually park?nson dusease can cause semptoma of depression , and delusional beleive , mostly in regards to wife infidelity and dementia. Treatments r not a cure.