Ugh, that's so awful. I'm really sorry that happened to you!
I agree that it's okay to sign up to Yuletide as a clean AO3 with no social media, though. Obviously you should make sure to write requests/a letter that are detailed enough that your writer will be able to write to your preferences without any outside reference... but really, everybody should be doing that anyway as a part of basic exchange etiquette. Anyone who gives you trouble for not having a presence beyond that is just being a weird asshole.
Re: Is an AO3 account not enough?
I agree that it's okay to sign up to Yuletide as a clean AO3 with no social media, though. Obviously you should make sure to write requests/a letter that are detailed enough that your writer will be able to write to your preferences without any outside reference... but really, everybody should be doing that anyway as a part of basic exchange etiquette. Anyone who gives you trouble for not having a presence beyond that is just being a weird asshole.