Hi Karen
There are a number of issues. I will try to address some of them for you.
Although she forgets the answers I do think it is important that your answers are consistent. It helps if there are a number of different people caregiving.
I think it is important to tell the truth but always be sensitive about its delivery, especially about people she has forgotten are dead etc.
Give short simple answers, complicated pieces of information will only increase her anxiety and confusion.
Remember that the brain damage that occurs with Alzheimer's is profound. Think of her communications with you as her brain is trying to compensate for the huge holes in her memory. Because of the brain damage it is unable to do so. That gives you a good idea of why she keeps repeating questions and concerns. It can be very frustrating for caregivers to deal with the resulting obsessional, repetitive interactions.
Anxiety is a very common for people with this terrible disease. It may be best to see a specialist gerontologist who can advise you and may suggest prescribing a mild tranquillizer which may help.
Reassure your mother, try to distract her, talk to her softly.
Try changing her evening routine.
Provide activities in the day so that she is tired before bedtime
Avoid assisting them to bed too early
Do not have stimulating activities before bedtime
A warm bath, soft music, may help relax them-so might a warm milky drink
Hope this helps
Christine