I can offer some possible explanations for her behavior, based on general human psychology and social dynamics.
Curiosity: It's possible that your ex-best friend is simply curious about what you're up to and is keeping tabs on your life through your Instagram stories. People can be naturally curious about the lives of others, even after a friendship ends.
Habit: If she used to follow you on Instagram when you were best friends, it's possible that she hasn't unfollowed you but may not actively engage with your posts anymore due to the change in the dynamic of your relationship.
Sentimental Value: Perhaps your ex-best friend still has some sentimental attachment to the memories you shared, which leads her to view your stories out of nostalgia or to feel connected to the past.
Avoiding Confrontation: Some people may avoid directly interacting with someone they used to be close to because it can be uncomfortable or awkward after a falling out or the end of a friendship. Viewing stories allows for a certain level of distance and avoids direct engagement.
No Negative Intent: It's essential not to jump to conclusions about her intentions. She might not have any intention of making fun of you; rather, her actions could be harmless and not meant to cause any harm.
If you find yourself bothered by her actions or have questions about the situation, it might be helpful to have an open and honest conversation with her, if you feel comfortable doing so. Communication can often lead to better understanding and clarity in situations like this. However, if the friendship ended on a negative note or if you don't feel comfortable reaching out, it's okay to focus on your own well-being and moving forward in a positive direction without dwelling on her actions.
Remember, people's behavior can be complex and influenced by various factors, and it's not always easy to discern the exact reasons behind their actions. Focus on surrounding yourself with supportive and caring individuals who contribute positively to your life.