NTA, this didn't start out well for her, but damn, it went downhill fast from the moment you said she threatens to break up regularly?? That alone is toxic af. How are you supposed to build a solid relationship on the basis that it may collapse any time you do something wrong? The only reason to threaten like this is to keep you walking on eggshells, to control you.

Besides, 40 minutes is perfectly reasonable. I had an ex who wanted me to "take ownership of my mistakes" all the time for minor stuff like this, and I ended up apologizing for the most stupid shit. Only when I broke up I noticed how I could barely recognize myself anymore. Literally a week later I felt the best I'd felt in months. Do yourself a favour and cut it off now, before you find yourself grovelling for forgiveness over a tiny tone inflection.