I rewatched Episode 1 and Heather knew. You can see it in her initial greeting of Monica at the snow day party, and then her toast carefully mentions “we’ve been trolled relentlessly for 3 years” or whatever. She knew Episode 1. (I kinda think Jen told her when she found out who replaced her in the cast.)

Ever since the burner account reveal, does anyone feel like some accounts, posts, or comments here / on the main subreddit is Monica? I can’t un-see it now, she’s prob been lurking Reddit for ages 😂