Getting harassed on Instagram. Need help.

Every year on my friends birthday, someone creates a fake account at exactly midnight and wishes her happy birthday and posts a few really creepy stories and tags her. It’s been happening for almost 6-7 years now. It’s extremely creepy and I’m not sure how to catch the person responsible. Could someone please help us out so we can find out who’s responsible and have them face the consequences. It’s extremely worrisome and every year she panics when her birthday rolls around.