mirtazapine help needed please

15mg mirtazapine psychosis Hey my 75 year old mother was put on 15mg mirtazapine And started getting huge confusion,she was on it one week I then put her on 7.5 for 3 days then took her of it she then got worse She started saying this was not her house and lots of crazy stuff like she owns her sisters house and lots of crazy stuff also paroniod. She is of it one week today but this is strange thing I need help with After 3 days off it she was perfect then day 4 back to being crazy then day 5 was ok again then day 6 crazy again . It this the waves and Windows I read about online How long will it last will she get better I'm very worried she never had any mental issues GP is useless he said oh must be dementia but it's from the med can any one put my mind at ease will she get better thank you
Her symptoms match with deleruim not dementia