Backround

I have a LTR of 6 months, we're both 19, she is totally into me, or used to be. For past months of our relationship sex is present each day, about 2-4 times per day on average. I do what I want to her in bed. She is my first girl to have sex with, although she was FWB at first, then got promoted for good behaviour and stuff

The problem

Recently she started taking offence for really dumb shit. I didn't get her milk from higher shelf (I was fucking with her to say "please get me the milk"), or today I texted her that I have 55% frequency on my French classes so I can chill till end of the year, on the contrary to her situation with math. Got mad and I told her that I'm not taking this shit and she can contact me when she gets over it. Silence for 6 hours. She argues that I do that in rude meanor and try to get her offended, while in reality I say everything with smile on my mouth. Also I supposedly don't know when to stop the joke (it might me truth when I think about it, but her period of time I can laugh at one thing is shorter and shorter).

What shall I do, keep frame up and punish her somehow, ignore her moods or is it lost case and 'next' is only way out?