To get through it, you need to stay centered on yourself and what you want to be, not on her. And I would recommend having an exit strategy as well - a plausible excuse (have to work the next morning? have animals to care for?) that will allow you to leave without saying you're leaving because you can't stand to be there anymore.
As for staying focused on you, there are two scenarios possible here:
1. You focus on her. In this scenario, you go to the party thinking thoughts like "I don't want to talk to her," "I'm still angry at her," "If only she were different." Every thought, and therefore action, reaction and emotion, has her at the center of it. This scenario will guarantee you a very unhappy experience.
2. You focus on you. In this scenario, you go to the party thinking thoughts like "What kind of person do I want to be?" "How do I want to treat the human beings in my life?" "How would I respond if this was a person I'd never met before?" In this scenario, you focus on yourself, your needs, your desires for what kind of person you want to be. You let go of trying to change or wanting to change or expecting change from your mother. By focusing on who you want to be, and not who she is, you put the control back in your own pocket.
You can't control her, you can't change her, but you can control and change yourself. By focusing on yourself, you can maintain control of the situation and be a happier person.