We are having difficulty because the person we are caring for is telling us and her visiting nurses things that are not true. Sometimes what she makes up are things that are alarming to us and others. She sometimes even makes awkward or hurtful claims about people that aren't true. The best we've done is to clarify the truth to those concerned but if we try to discuss the truth with her she gets angry or upset.
I would check to make sure that what she is describing is not true, though. Since, she isn't in touch with reality, I'd ensure that some trusted person supervises her for her own safety. You can't really convince her she's wrong. You might also check out some videos on you tube by Teepa Snow about managing someone with dementia.
https://www.agingcare.com/articles/how-to-handle-alzheimers-disease-lying-144204.htm
Dementia/Alzheimer's is a very difficult thing to deal with, for all concerned. Hopefully the article gives you some useful tips to help you navigate the stories she's telling.
Good luck!