How should I respond to : I'm sorry I was a bitch yesterday. I was cranky

She was infact being a bitch, and so I stop responding, which usually enough to illicit an apology when she presents bad behavior.

She often will apologized for either real or imagined transgressions. For example:

She asked how much I had left to do for a homework question. I told her one more question. She said something irrelevant and I responded with uhhh yeah. And she freaked out, quickly apologizing and saying she regretted the moment she asked how much was left.

Then for the real transgressions an example was her stepping boundaries.

How do I handle those apologies? I don't want an apology, I want her to stop what creates the incessant apologizing. How would I go about that? Considering being direct doesn't always result in the results you want.