My Mum also used to be a teacher. Looking back the first clue to her Alzheimer's, before diagnosis, was the loss of concentration for reading.
One year on holiday she didn't bring any books, which was most unlike her, but just bought a couple of magazines at the airport and sat idly turning the pages for two weeks.
Her diagnosis didn't seem to bother her, she dismissed it saying she was just a bit forgetful which was only to be expected at her age.
The main problem we had was that she refused to have any outside help, insisting my Dad did everything. We all lived too far away to help regularly and he was exhausted.
Eventually she had a bad fall and a lengthy hospital stay.
A super social worker insisted on home care being put in place before Mum could be discharged.
If Mum and Dad hadn't agreed, the social worker told me I could overrule them as I had power of attorney. Thankfully it didn't come to that.
Dad benefitted so much from this and they both became very fond of the lovely carer, who was with them until Mum died peacefully at home.