I'm the one with dementia is my family. When I'm told that I don't remember something (or that I'm remembering something that never happened), I feel really sad or completely argumentative as i CLEARLY remember something (even if they tell me I'm wrong). I absolutely hate sentences that begin with "don't you remember...", because it points out to me, once again(!) that my brain is going away. If you can, try not to remind her of what you know happened. If she asks, be prepared for her sadness or anger if you decide to tell her the truth. I've noticed that my caregiver is beginning to lie to me and i HATE it. I asked why and he said it's because I get sad or mad each time when i ask him something and he reminds me of the reality. I hope you find something that works with your loved one. Personally, I'd rather the truth than a lie... even if it makes me sad-- but that's just me.