thanks for your question
Dementia is really a serious condition in elderly. Your mother is feeling low, having paranoid ideation and is constantly upset. I hope she is not having much motor symptoms or there are under control.
xl in 300 mg is a very nice drug to control low mood and other behavioral symptoms but you can discuss with her attending doctor to start SSRI drugs like Sertaline in low doses which are more potent thank bupropion
How is her sleep? If she is having good sound sleep (5-7hrs) then there is no need to stop zopliclone as stopping will worsen the condition and may cause rebound insomnia and will worsen behavioral problems.
Regarding her paranoid ideation I think her doctor is not giving proper prescription as you can discuss with him to start some low dose Second Generation Antipsychotic
drug like olanzapine
or clozapine (last modality) which are comparatively safer in Lewy Body dementia.
So as per my advise kindly do not stress on stopping drug instead ask the doctor to review prescription to start more potent medicines and to start medicine that cover paranoid ideation
thanks hope i solved your query