There are so many wrongs in this picture that I do not know where to begin.
First of all, if you cannot get someone else to take this ticket, then, yes, she should reimburse you. But, I don't see that happening.
To tell you that you should not go because she can't? Seriously? Um, yeah, special snowflake here. First of all, it is not that she can't go. She chose not to go. She chose to make other plans. I have to wonder where her brain is at that she still thinks you should not go because she made other plans and is not going with you?
There is no way I would make plans with the gal ever again unless she apologized and paid for her ticket without even being asked to do so. Just because you are in a group of friends does not mean you have to be friends outside that group.
And I am getting mean in my old age, or it could be PMS, but I am so tired of people getting away with crap and always being the bigger person. If anyone asked why I wasn't exactly friendly towards this person any longer, I would tell them exactly what happened, especially if she would bring something up in a group event.