So, finally finished reading the last arc of Supergirl recently. It wasn't my favorite, but there's an epilogue at the end where she cuts herself by accident and bleeds, questioning what might be happening.
My best guess is that this is connected to the Truth storyline for Superman and his powers becoming more limited. I haven't seen a lot of discussion surrounding this, but I find it interesting that whatever is going on with him might be occurring for all Kryptonians.