Well John, there's a few more things you can try...................have a sit down/phone her family doctor and discuss your concerns..............that way he can watch out for any signs at her next visit.
Also check the family tree......ask an older family member about her parents/siblings..........genetics is a powerful thing and so are family "secrets".............it might take some digging, but the clues are there...................possible early on set alzheimers
There are supplements that help with memory and with mood, however the next problem would be getting her to take them..............there's only so much a person can do