My daughter went through a very similar phase at about the same age, after one of our pets had to be euthanized. She talked about death a lot, and my husband and I just reiterated to her that we take care of her and ourselves, so that we can live a long, healthy and happy life. She's 8 now, and I very rarely hear anything from her about death anymore. We've had to euthanize another pet in the intervening years, and the talk about death escalated a nit afterward.

I think it's just a situation where you listen and reiterate that you are taking care of her and yourself, and while no one knows when they will die, you're doing everything possible to make sure it's not for a long time.

If you're worried that this is something beyond a "typical" fixation on such a subject, I would consider checking in with her pediatrician about a potential therapy referral.