Its a good thing. You'd have to give us more context, but typically when this happens, its because she consciously shit tested you by requesting something unreasonable of you or otherwise being disrespectful/rude. The reason she apologizes is because she knew from the start that what she was doing was "wrong"/socially uncaliberated.
Ex. This happened to me about a week ago:
Her: Buy me ice cream!
Me: [laughs] No, I think you should buy it yourself.
Her: Yeah, you're right I probably should. Sorry about that. <----Not sure if those were her exact words, but that was the gist of it.
So the answer is, no the apology itself isn't an act. But whatever it is that she's apologizing for probably was.