I would perhaps say that she now ‘struggles to recognise people, even close family’, rather than that she has ‘forgotten just her. It would be easier to hear and is also possibly closer to the truth. Advanced dementia includes all kinds of issues with visual and aural recognition. I, personally, do not feel that ‘forgetting’ is the right word to describe this.
My husband certainly often did not seem to recognise anyone for a year or two at the end but his very last words when he opened his eyes and saw his daughter a few days before death were ‘very nice’. The most lucid he had been in a very long time.