She's bullying you. The consequence for that in my house would be,
"You are clearly having trouble keeping unkind thoughts in your head, and you're not mature enough yet to understand what will and won't hurt someone.
"That's OK, it does take a while for empathy to develop in some people. We all struggle to learn things sometimes.
"But you have really, really hurt me, and I can't let you hurt other people like that. So I will be talking to your teacher at school. I'll tell them what you have been saying to me at home and asking them to keep a closer eye on what you are saying and doing at school, so they can help you if more unkind words accidentally come out.
"Until I can trust that you understand that words have consequences, you won't be going to your friends' houses or out with them, because I can't trust you to be kind, and I'll take your phone now please for the same reason.
"You said that you called me fat because it's the truth and I am fat. I want you to have a think about why that might upset me, and we can get together the same time tomorrow and you can tell me the reasons you've come up with. I want to see if you understand what upsets people because there might be something different about the way you look at the world that we'd need to talk to someone else about."
I'd hold this as a very firm boundary. She wouldn't be seeing anyone outside of school or using her phone until she could be trusted, and I'd want school to keep an eye on her behaviour to make sure it's not the start of something awful. I'd tell her we'd review things every month until she had learned how to be kind.
Then I'd fire your husband into the sun for laughing with her.
I am so, so sorry your daughter did this.