Not at all chelseagirl, Im afraid its only too common with dementia.
She is forgetting about her home and dosnt recognise it now. Quite often people with dementia say they want to go home, but actually what they mean is that they want to go back to a time and place where they werent confused (and often scared).
When she says this, it wont work if you try and persuade her that it is her home. Can you change the subject and talk about something else when this happens? Please dont blame yourself
If distraction doesn't work, you could try telling her you'll take her tomorrow.
I often said this to my mother when she was wanting to go home to her long-dead parents. We couldn't go today because the roads were very busy/icy/the main road was closed because of a bad accident/my car was being serviced, you name it, I had any number of fib-reasons. But they always pacified her for the moment and she never remembered that I'd said much the same before. If your mum's short term memory is also very bad you would very likely find the same.
Whatever, it is most definitely not your fault - it's the beastly dementia.
Dear Chelsea Girl,
it is not your fault. Your mum cannot make sense of reality because of the dementia and is wanting to return to a time and place where she felt safe. As others have said this is quite common but it does not make it less distressing to not be able to fix things for someone you love.
It might work to distract her with music. My mum was always cheered up by the hits of her youth and when she got agitated on the day she died I managed to calm her by singing songs she had sung to me as a child. Scarlet Ribbons was and Golden Slumbers calmed her.