Dan,do still visit your aunt, you don't need to lie, just move the conversation on with " I am sure she is missing you too" or something similar. My mother has dementia and never asks about my father anymore, although she remembers him, they were married 67 years. She talks about him and recognises his photo, I think deep down she knows he has passed away but after the first weeks of grief she seems to have moved on .However my brother had a heart attack a few weeks ago, he is the apple of her eye and saw her 4 times a week. I was dreading telling her he was ill. The first week I said he had car trouble and she accepted that and didn't ask again where he was.He has only seen her once a week but she does not appear to miss him.
Dementia affects people in so many different ways but one thing I am sure of is that they will never react the way you expect! Three golden rules, be guided by them, never disagree , and don't ask any direct questions. Very difficult to do but it does work!

Your relationship with your aunt is important to you both, just visit and talk about mutual memories , or just hold her hand.She loves you and will be happy to see you.

with love Wendy xxxxx