Have to see old roommate [24 F] that I [23 F] ghosted. How to handle possible confrontation?

So I sort of had a mental breakdown this past year that started while I happened to be living with this girl. (I'll call her Sarah) A lot of things happened with my dad getting very sick and I had a crisis about my work/self. I've been unemployed this past year but I'm starting to feel myself shake off this depression and get back on my feet.

Anyways, this girl might be the most two-faced person I've ever met. She is always gossiping about everyone all the time. It made me feel incredibly paranoid while I was living with her. More than a few times I ended up hearing stuff she'd said about me. She would also say very insensitive things to me all while acting weirdly innocent, like she had no idea it was rude unless I pointed it out. I started ghosting her while we were still living together and the moment I moved out I never said one word to her again.

We share a lot of mutual friends and they would mention her from time to time but I think they know I've chosen to cut her off. I vented to them a couple times while we were still living together but never the true extent of how horrible this girl made me feel. I never explained why I cut her off because that felt too much like I was shit-talking and I didn't want to do that.

So here's why I have to see her again. My good friend is have visa issues and is leaving the country next week. She's throwing a huge party so she can see everyone one last time. Usually I would just skip if I knew Sarah was there but I really want to be there for my friend this time. I'm pretty horrible with confrontation and usually just end being as nice as possible as a defense mechanism. I'm afraid she might use this to try and come back into my life again. If I do talk to her again and I can almost certainly expect some snarky comment about my unemployment status. She might also ignore me as she's prone to giving people the silent treatment when she's mad at them (I'm honestly hoping for this). Usually my boyfriend will help me out with this stuff but I don't want to have to keep him tethered to me the whole night. I don't want any real confrontation as this is my friend's goodbye party and I want to focus on her. Does anyone have any tips or tricks for dealing with a situation like this?

tl;dr: Have to see old toxic roommate at a party I can't miss. Looking for any tips on how to deal with this girl. Maybe just some coaching to psych myself up before having to interact with her again.