Is this woman testing me? Why would she have cancelled rudely and with attitude?

This is little more than conjecture on my part but I don't believe she was angry about anything. From what I gather the two of you go to the same gym, have spoken a number of times, perhaps there was some friendly flirting. Did you know about her boyfriend prior asking her to get together? Maybe she's not ready to come to terms with her true feelings so rather than outright reject you she came up with a decidedly lame excuse. You're right, doctor's appointments tend not to go that deep into the evening. And like most people, she probably does hate cancelling on someone.