Ignore how her family are coping. Perhaps the care and love you show your friend will enable her family to follow your lead. Dementia doesn't come with a handbook, the professionals seem to disappear into thin air and we see all left to cope as best we can.
Your friend is very lucky to have you. Ignore the idiot do gooders looking down their noses. If things get really bad in the future you could print off some small cards and hand one over.
Later on I would be tempted to write 'my friend has a terminal illness which is effecting her brain'. If that doesn't shut people up nothing will.