So called best mate 👎🏻

So me and this girl have been friends for a few years and we are super close with each other. However I seem to always put her first and I always seem to be put second with her. Recently she's been getting mad with me for silly reasons, I'm going to Uni in September and she isn't and I'm meeting up with a girl I'll be going to uni with and she was acting really annoyed I thought she was just trying to be funny but now I think she might actually be annoyed at me for this. I don't know what to do, every time I try to speak she ignores me and do I don't know what to do.

Any advice?