How about I ask my girlfriend to unfollow a guy on Instagram who she had an incident with?
Interesting. Why do you want to ask her to unfollow him?
She's been lying about who she is and she needs to admit it in front of him.
Your partner has a right to follow who she wants. You should refrain from monitoring her Instagram account. It's none of your business and will lead to controlling behavior.
I don't care, she needs to listen to me.
I think you're in a deep state of denial and this needs to be stopped. This is a deeply controlling situation and will be toxic if not remedied right away.