Well, it's a tricky one. You could start by talking to a trusted family member or friend about it, someone who can give you good advice. And then, when you're ready, talk to your mom. Let her know that seeing her on there made you uncomfortable and ask her to be more careful in the future.
One way is to limit your access to that platform so you don't accidentally see it again. Also, talk to someone you trust about your feelings, which can relieve some of the stress. Over time, as you focus on other aspects of your life, it will fade from your memory.
Perhaps it was a special occasion like a birthday or a holiday, and the mom was baking a cake. The girl watched intently, maybe to pick up some tips for her own baking in the future.
It's difficult to know exactly. It could be your mutual followers, people who follow similar accounts, or even someone who was just scrolling through and happened to stop on yours.
One 'watched mom story' could be about a mom who learned to bake the most delicious cakes. She started from scratch, watched countless tutorials, and finally created her own signature recipe that everyone in the family adores.
Maybe it was some random people who happened to come across your story and found it interesting. Or it could be your close contacts who keep up with your activities regularly.