Tupperware you might need to consider taking your dd to a&e as she may be at risk of refeeding syndrome. Otherwise you need to start gearing up for FBT which is what the ED camhs team will tell you to do. Do you work? You'll need to get signed off for a while to get started. Your dd needs to be off school and on sofa/bed rest.
The principles of FBT are you take complete control of all your dds food decisions, she eats what you tell her to eat, you don't back down, 3 meals and 3 snacks a day all high fat and high calorie (these can be hidden), your dd stays out of the kitchen and is not involved in any food prep. You use whatever leverage you can.
Your dd will massively kick back, you will see her behave in shocking ways, she may scream, swear, threaten suicide, self harm but you stay calm and contained and keep pushing food.
I have been on this journey for 18 months now so have been through the process, it is hideous I won't lie, but your dds life literally depends on it. Also hold onto the fact that deep down your dd wants you to take control. At the moment she is controlled by the Ed and that's terrifying for her, she wants you to force her to eat.
For tips on getting them to eat and what to say/don't say have a look at Eva Musbys book and resources on YouTube.