Yes you need to set boundaries and choose your battles but I think it’s a mistake to suddenly ramp up discipline op in response to her current behaviour.
You need to ease off with the top down parenting approach and switch to parenting alongside her, helping her to develop her own self discipline by giving her more responsibility. You are there to support her working out things for herself not to micro-manage.
Don’t let her get away with being too disrespectful but equally the best thing to do is ignore most of the rudeness and focus on keeping things fairly calm and positive and focus on your agreed top three parenting priorities.
And above all, model the habits that you want her to copy. This is the stage of life when they start to view us with a more critical eye. So if you want her to eat healthily, work hard at school, exercise, then you have to do those things too, if you are not doing so already, otherwise you will have no authority whatsoever. Remember, all teens love to hate a hypocrite! 😉
This is a marathon not a sprint and unfortunately part of your role is to be an emotional shock absorber when her feelings get temporarily too overwhelming so make sure you exercise and eat well and boost yourself up for the next five years, by which time you should be through the worst! 😫🤨😁💪
Don’t get drawn in to a downward spiral of negative back chat; do fun things with her too - keep it all humorous and affectionate - yes they still need to know they are loved. Probably more so when they are being a pita.
What she is going through is a totally normal transition when her brain is in a state of plasticity, a bit like a toddler. So don’t take the rudeness personally as she is incapable of discerning how hurtful she is being. And it’s hell for her too. When she is at her stroppiest, she is probably feeling massively insecure. Listen to the emotion behind the words, not the words themselves !
Just step back a bit and be a bit less available when she has been horrible. And don’t punish her for hiding in her room, that’s the first ‘safe’ stage in splitting yourself off from your parents. Be prepared for her to be rowing one moment and totally fine the next as if nothing ever happened. Always start each day fresh!
Do keep an eye on her eating. Maybe cook together as a pp suggested. Keep the lines of communication open and be very careful how you speak to her about food and weight. Let her gp weigh her and ask any awkward questions. You be the safe space.
I’d keep the battles away from table and take as much pressure off meals as possible. Just for this period while she’s going through a difficult phase. You could prepare healthy bowls of pasta or healthy snacks for the fridge that she can grab when she wants. Lots of fruit and yoghurt. And don’t forget red meat, or iron heavy vegetarian equivalents like chickpeas, broccoli and pulses as she’s menstruating.
I recommend the books on parenting teen girls by Lisa Damour.
Good luck!