When a girl says she'll let you know later on, but doesn't, should I be mad?

Anonymous
This girl I've been dating, we talk about everyday and yesterday I asked her if she had time to get some lunch because some stuff is going on with her recently and we've been kinda distant so I wanted to just talk to her really, in person not texting or over the phone. I know she knew that's why I asked her to lunch, but about 30 minutes before, she texts me taht she's really busy and if she can just see me tonight. I said that's fine just let me know what time she gets off work, and she said, "ok I'll let you know" she told me this like 2x adding in once, "thanks for always being there for me" so night rolls around, no text or any type of response, so I just went to sleep and I'm kinda p*ssed she didn't even have the decency to text or tell me that she got off work too late and didn't have time to see me that night. and I would of just let it go and write it off as she forgot maybe, it happens, but obviously she's on facebook and sh*t writing on guys walls about random crap so its kinda hard to just say she forgot. I'm kinda p*ssed that she didn't even text me the next morning say, sorry I forgot or I was really tired. Do I have a right to be mad at this?
When a girl says she'll let you know later on, but doesn't, should I be mad?
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