My mother has been diagnosed with mild dementia

[enough]

8. Having lived through both my parents' last years with dementia, and now

not that much younger than your mother, I would say:

1) Don't try to figure out what the doctor meant without talking to the doctor. If you are concerned about it, go with her/them to the next appointment and the next one after that. If you can't do that, call the doctor, who may or may not be willing to talk to you.

2) Do talk with your mother and find out what she thinks is going on. If it's actually dementia, you may not have that much more time to have this kind of talk with her. But at this point I wouldn't start from the assumption that it's dementia.

3) Try as much as you can to relate to your mother at this point just as she is. Don't get panicked by what you have heard from your father and about which he may also be panicked.

4) Remember that you (and all of us) are on a moving current. What's happening now is not what will be happening later. Have as many direct conversations and ask as many direct questions as you possibly can now, and at all future moments.