Oof. I have very little experience with this side of the situation. I’m usually the one my loved ones are worrying about. I always say that I have the easier role than they have. From the other point of view, I’d say that she does not want you to be scared. Much, much, much easier said than done of course. Surely she feels she must try to be hopeful, and she wants you to be able to feel hopeful too.
As @Coloma says, and as it has taken me a very long time to figure out, worrying is a rather useless activity. Of course it happens naturally in these sorts of situations. But it happens by choice sometimes too. I’ve recently made the realization that I spend a lot of time feeling like I must worry. Do you ever feel this way as well? I must worry, it is my responsibility to do so. If I really care about my mother, then I must worry about her when she might be ill. I need to have a game plan for when things go wrong, so I must think about what might go wrong and plan for the worst. I must worry about things that haven’t happened yet and may never happen. Therapy is helping me with this. Worry is, in truth, independent of the physical world; it’s all in your head. This seems obvious, but I know I’ve felt on some level in the past that I must worry, must pay scary situations my attention, or they will progress outside my control. The truth is, they progess outside your control whether you worry or not. The worry can have some pretty awful physical and mental effects on you too, if it’s spread out over a long time.
For now, spend some good time with your mother, try to laugh, and try to keep your mind in the here and now instead of in the millions of possible futures that may await you tomorrow. Wun day atta time. :)