I don't know you well enough to suggest whether to go or not, Crys, but does your friend know how you feel? If she's a good friend, she'd understand and either guarantee she'll go or suggest you meet up another time. If she's keen to meet lots of the others, then the latter may work better for both of you. I'm sure she wouldn't want you to be uncomfortable.
I was invited to a weekend away reunion (25 years on) by a group from school whom I'd always regarded as very much NOT friends. I decided to go, because it meant I could see the plague village of Eyam while there, and I wanted (perversely) for them to see I'd done OK for myself. I discovered a lot about my misconceptions of how they'd viewed me at school. One was envious of the dad I had (hers had apparently been not the best, although I knew mine wasn't perfect!) and my big academic rival, who, I thought, had had no time for me, said her lasting memory was of me rescuing her in a language lesson (just 2 of us in the class) where the teacher (whose pet she always seemed to be) was being harsh. She'd been unable to translate something and the teacher only let up and allowed me to help when rival was in floods of tears.
I then proceeded to translate for the rest of the lesson while she composed herself.
You just never know.