It doesn't make sense? (advice)?

I've been in a long distance relationship with a girl for 1.5 years. We were FINALLY gonna meet in 26 days, and she was super excited.

Then we got into a few fights (the fight was about lack of time together and whether I fit into her life at all because she was freaking about how how she's young and can't put me first in her life) two weeks ago and we took a 6-day long break. Now she doesn't want to be with me anymore, at all. It makes no sense to me. She said it herself, she was crazy in love me just a two weeks ago. I don't understand what could have happened that drastically changed everything so badly? She said that the fights over those two weeks took a lot of energy and motivation out of her to be with me. But am I naive to think that it's impossible for a two-week fallout to entirely trump 1.5 years of love?

I told her to just test the waters out when we meet up for the first time, but she doesn't even want to do that? To me, it makes no sense. Absolutely none.

Her other reason was that she's young and doesn't want to be tied down so early (she's 18 and I'm 21, though she led me to believe that she was my age up until about 7 weeks ago when I bought the ticket and needed her birthdate). I was confused by the "tied down" part so I said " 'tied down' as in 1) you don't want to commit because you feel like you won't be able to do a lot in life? Or 2) you don't want to commit because you don't know where this relationship could go, or if it could go on?" and she said number two. I assured her that I never intended for this to stay long distance for long.

But her youth just doesn't make sense because her sister met her boyfriend in their teens and now they're married, just bought a new house. And they're starting a family. I pointed that out to her, and that led her to pretty much say she doesn't know if she wants to be with me anymore period. Over the course of this fiasco, she has brought up her youth several times so then again it could be a factor after all - not as in I'm too old for her, but just that her life is a head of her, I think.

It's mind boggling. At first, I thought the logical answer would be that she found someone new, in person. But that doesn't make sense because we've texted and skyped from sunrise to sunset. And of our brief break, she spent one day playing the video game we met on, and then she spent the rest moving into her new house with her sister (which I'm 98% is true because she told me weeks in advance that those days were the days, so she could not have met anyone new).

It makes no sense to me. We were so close, why would she NOT want to take the shot to meet up with me in 26 days to judge this relationship at face value? I tried to talk sense into her, but she hasn't listened to any of it AT ALL.

It's also worth noting that she was the one, from the beginning, that wanted this to be serious.

Last year at this time, I tried to break up with her because I never thought we'd ever meet up at all, so I figured why continue? I tried to back out, thinking this would go no where. But she fought, I listened, and we lasted a year longer.

I don't know what to do anymore if I can't even talk sense into her. Advice, Please.

Also: I've have thoughts of forwarding her the itinerary to the $460 plane ticket I bought her (she had asked to see it when I bought it for her, but I didn't show her at first because it was on my laptop not my iPhone. I was planning on forwarding it to her the week before she left for here since she'd need the itinerary to board the plane) and saying something… I dunno.probably SOMETHING. Maybe "Here's the ticket. You can come, but you don't have to. I really do wish you would just take a look into our relationship before dooming it" or something like that. Would this be a good idea?

Maybe she just wanted an Internet thing and them when things got real she backed of take your losses and find someone in your area next time