It could be that the app needs an update. Sometimes outdated versions can cause crashes. Also, conflicts with other apps on your device might be the reason.
It could be that they haven't fully moved on and are keeping tabs on you. Or they might just be bored and randomly scrolling through stories, and yours happened to catch their eye.
There could be several reasons. Maybe your stories are unique, funny, or inspiring. Or maybe she considers you a friend and wants to show support by viewing your stories regularly.