as you have mention that she acts very agrresively and start blaming others when she stop medication.
important part in diagnosis is her total symptoms profile, initially and during last 2 yrs which type of symptoms she had.
if blaming behavior is without any base and if at delusional level then only it is a psychotic symptoms.
please meet 1 psychiatrist
in palce near to you with your sister, so her proper diagnosis and treatment will start.
and your second question about wt gain- ziprasidone
, aripripazole, amisulpride are the medication without side effect of wt gain
in which aripriprazole and amisulpride is good option for better symptom control.