WTF just happened?!?!

So I totally was studying for the day. No issues, my gal wanted to go the the pool over at her friends, still no issue. all of a sudden, bam! I asked if we could hang out when I wanted to take a break, and she got pissed. She started calling me possessive and etc. I calmly tried to understand where she was coming from. I just wanted to know if she was cool with me coming to see her when I was ready to take a break. Instead of saying i need my space she yelled at me. I automatically tried to talk with her and calm her down. I hate when she is upset, no matter who it's at. My mistake in all this was i lost my patience. I took our cooler radio out of her truck which was just as stupid as her yelling at me for no reason was. Then she got in her truck and started to drive off and i pushed in her mirror. I never punched it, just pushed it because i was just wanting to understand why she snapped like that. It broke the mirror, which was not at all my intention, and cut me. What cut me the most was she was sure that i was being possessive. Not at all, i simply wanted to spend an hour or so with her during a break because i knew this weekend we wouldnt see much of each other. So i think for now I am just going to leave her be, and maybe she will understand that my intentions were merely to spend a bit of time with her, not at all was i denying her needs to go hang with her friends. I just wish she knew, I understand her needs, i just don't understand her anger. Couldnt she have calmly said, baby, i just need me time today... ok no problem.