My gf wants both of us to die

Context. I have a suicidal past and my significant other has that as well.

She asked me 20 minutes ago if after we end our horse caring job we’ll go climb a near by cliff (40 meters in height) and jump together. I said yes jokingly but she told me she’s serious I’m 100% sure she wants to but I don’t really want at this point.

I know her well enough to know I can’t convince her not to plan something and she told me she won’t go to the psychiatric ward ever again.

I know I should call the police but I don’t want to make her unhappy (If that makes sense)

What should I do?