It's all about power struggle. You give her power every time there's even a hint that you care what/how much she's eating. You need to take this away by not caring if she eats or not. Even if you're dying inside that she's not eating. Yes, it's hard, but it definitely works.
Your job is to provide food. Her job is to either eat it or not. Just serve her what you normally would. Unless she has any medical needs, SEN or is under dietician, she won't starve herself.
She might reject a few meals, but once she realises it's pointless, she'll start eating. "This is what we're having today, you don't have to eat it if you don't like it, but there's nothing else".
If she throws a tantrum, remove her from the table and tell her she can come back once she's able to behave.
Don't cajole, threaten, or bribe with pudding, don't praise if she's eating. Chat about your day, or plans ahead, or whatever.
I found a good way to get them to try new foods is put all food out on the table in serving bowls so that they can help themselves to what they like the look of. It gives them a feeling that they are the ones in control.
I would really recommend "Getting Little Blighters to Eat" book if you want to read more on the topic.