DSis has a long history of becoming passionate about a cause (usually involving animal rights), posting lots on social media, circulating petitions etc, until it fizzles out and she takes up another cause. She's never taken much interest in politics or world affairs.
Last year she took up a political cause and since then she has started believing in various conspiracy theories. Some of what she now seems to believe is quite outlandish. A couple of weeks ago she told us that if she disappears or dies suddenly it will be because "they" have got her.
A couple of family members are very worried about her mental health, but others think this is just the latest cause and will blow over.
She has a good job, but has been WFH since lockdown, so she doesn't have work colleagues who would notice anything. Her social media is bizarre but I think most people muted her a long time ago; no-body seems to interact with her.
At what point should we, her family become worried?