It could mean she's not ready to have a direct conversation with you yet. Maybe she's shy or doesn't know how to respond to your texts. But she's still interested in what you're up to, so she watches your stories.
Send her a story that's a bit more personal or has a question in it. For example, you could post a picture of a place you like and say 'I wonder if anyone else likes this place as much as I do?'. This might pique her interest and make her more likely to respond to you directly. Since she watches your stories, it's a way to engage her without the pressure of a direct text.
It could mean that they still have some level of interest in your life but don't want to directly interact. Maybe they're not over you completely and are using your stories as a way to keep tabs without getting too involved.
There's also a possibility that she's conflicted. She might have some reasons for not wanting to interact with you directly, like she's currently focused on other things in her life such as her studies or career. But at the same time, she still has a bit of an interest in you which is why she watches your stories. It could also be that she enjoys the anonymity of just observing your stories without the pressure of having to respond to you.
Yes, you could approach her. Since she watches your stories, there's a chance she's open to some form of communication. Just be casual and friendly when you do.
It could mean they're shy or not ready to directly interact. Maybe they're interested in your life but lack the confidence to engage with you personally.