She might be in a state of conflict. On one hand, she blocked you perhaps because of a fight or some negative feelings. But on the other hand, she's not fully ready to let go and still wants to keep an eye on you. It could also be that she doesn't want you to be able to directly interact with her, but she enjoys passively observing your updates.
Well, she might be having second thoughts. She ghosted you perhaps in a moment of confusion or because she thought it was the best thing to do at that time. But now, by watching your stories, she could be subconsciously missing you or just trying to keep tabs on you without fully committing to a conversation.
It could mean she still has some curiosity about your life. Maybe she doesn't completely want to cut off all connections with you, even though she ended the relationship. It might also be a habit. She used to be interested in your stories, and it's not easy for her to just stop all at once.
Well, it's a bit complicated. She might have rejected you for a particular reason at that moment, like not being ready for a relationship or having other priorities. But her watching your stories could indicate that she's not entirely indifferent to you. It could also be a subconscious thing, where she's used to seeing your updates and just continues to do so without really thinking about the implications. Or perhaps she's having second thoughts about her rejection but isn't sure how to approach you again, so she just watches your stories for now to see how you're doing.
You could try to respect her decision to block you and just continue living your life. If she's interested in your stories, she might come around on her own. Don't push the situation by trying to contact her through other means.
She might be simply nosy. Just because she ended the relationship doesn't mean she doesn't want to know what's going on in your world. It could be that she has a habit of looking at people's stories and yours is just one of them.