Yeah, it's just coincidence that the very second that I explain that it upset me that a girl who lives at home and doesn't have to do chores, and has no plans for tonight is busy for 4 hours doing something more important that apologising for being a bit of a penis.

The passive aggressive bit was actually about how she usually acts a day or so afterward.

As it happens, this time 4 hours later she did contact me back, to tell me about a guy hitting on her (totally not passive aggressive).

Fortunately I took the advice given above to be a bit more assertive and called her up to ask what the fuck she was doing and the fact that instead of trying to apologise, she disappears for hours only to tell me about dudes hitting on her. I told her it made me wonder how seriously she's taking me, our relationship and my feelings; and that it's important for our future that it's not just me making an effort to fix things between us.

She got in contact with me a bit later to apologise properly for being a dick and that she understood that we need to work together each time we disagree or screw up.

Hey presto, no passive aggression, an honest apology, and hopefully no more of this shit.