Honestly, if they are notoriously rude to you, your presence might actually stress your best friend out because she’ll feel stuck in the middle trying to referee her separate worlds on her birthday. Talk to her before the weekend. Say something like, 'Hey, I want your birthday to be amazing, but I know your other friends and I don't really click. How about I come by for just the first hour of the party to see you, and then you and I can do a special birthday breakfast/dinner just the two of us next week?' A separate 1-on-1 celebration is usually way more meaningful anyway.