She's a teenager and you're stuck in the house together!
Her attitude is clearly unacceptable, I'm not saying you should put up with it.
Maybe her accusation about her working harder than you stems from stress over her exams and immediate future?
You're used to juggling different stresses and your job against everything else, but I still remember so easily how intense those exam periods were. How your entire future hung off just a few short hours. There wasn't any room for anything else - and in fact, when parents and teachers kept hammering it home how many hours you should be putting into preparing for exams...We were left with the idea that nothing else was as important.
Can't imagine how scary it must be to do it under lockdown, after a year of lockdowns!
Having said that, absolutely no judgement for losing your temper - my parents would have done the same.
Don't worry about her bitching to her maths tutor, they're not going to take her word for it!
I think you might just have to grit your teeth and see it through, you sound like a great mum. Soon she'll be off to uni and ringing you in tears whenever she's getting stressed about assignments and exams instead of storming out 
You'll get your lovely daughter back agaim and she'll realise all you've done for her.