Does your therapist extend your sessions to make up for the time? If not, I'd definitely be bothered by it. (My T is very prompt, but my marriage counselor is often late.) As for the cancelling last minute a few times in the last few months--that makes me think maybe something is going on in the T's personal life, like emergency-type stuff. Or maybe that the T herself is having some sort of health issue and is cancelling because she's not feeling well?

I'd definitely bring it up. If you have trouble talking about it, maybe send an e-mail or type it out and hand it to her at the start of a session. I doubt it's anything personal--she might just be really bad at time management. (I'm someone who is also bad at that and often run late, so I'm more understanding of that in others.) Are you the first appointment of the day? First after lunch? (Just guessing because you said no client before you.) If so, maybe try switching appointment times, if that's possible in your schedule.