Who's in the wrong in this, me or my friend?

From that, I would say that she is the wrong one. For starters, you did make the arrangements for her and told her about it. She had said no- from what I'm getting, when she said this, she didn't want you to know but she wanted to go with those people leaving you out. It is NOT your fault and from the last text, " She later texted me stating "I don't mean to make you feel unwelcome to go .. " you really should bring it up. But, no, you did NOTHING wrong. She was just being quite rude to you.