What do you do or would do?

I agree with both Amylynne and PhpPhoenix.
But there are ways of changing how one feels about a person, and sometimes how they feel about us.

It's rare for these things to change suddenly. I do remember one such occasion. After my father died, the housemistress unwittingly sent one of the girls I most hated (she was a bully) to comfort me. She was the only girl in the school whose father had also died. She held me hand and told me how it had been for her - and there was nothing but kindness in her manner.
In that instance, inside myself, I forgave her for every nasty thing she'd ever said.

Here are some things to consider which [i]might[/i] help:
What are her good qualities?
Why she might behave the way she does?
What might be her needs?

In some moment when there's no one else around (say, in the kitchen helping with a task), ask her about her interests, draw her out a bit, find out a little more about what kind of person she is.
If you share anything incommon, perhaps mention it.
Some people hate being asked questions; they think it's nosy or it brings up anxieties about being evaluated and judged, so if she seems reluctant or evasive about answering, shift to a lighter, more immediate topic.
Ask her what would be her ideal birthday, and how things are going so far.
(If possible, tell her friends so they can help make it possible.)

*
or go internal and consider things from your side.
What about the way she treats you bothers you?
Is it only that I feel the need to be liked by everyone?
Why is this important to me?
Is it that I want the whole group to get along?

Ultimately we cannot control others.
It's not possible to be liked by everyone.

It is possible to learn to unconditionally respect everyone, and to develop an attitude of openness and caring for their well-being.
One basis for this is simply that everyone has feelings and needs.
The path towards unconditional loving-kindness is an excellent one, but it's also close to saintly and not many achieve it.

If it doesn't work out the way you'd prefer, maybe try to just accept that it's okay if sometimes we don't like a person and vice versa.

If the party is large enough to "avoid" her, that's what I would do. I mean, not going out of my way to avoid her, but mingle with other people instead and give her a chance to do the same if she doesn't want to talk with you.

I'd ignore the person. I don't want to make anyone uncomfortable, but I don't care to try changing anyone's minds about me.

I only go where i feel enthusiastically welcome.
You dont HAVE to go to this event.

Stab her ?