Melt down

I am a dad to a 9y/o daughter with autism. It’s a new diagnosis, not particularly new behaviors but just now tying to learn. She has melt downs when she’s mad. I don’t think I need to describe them to the group- it’s hard. My wife is a master at avoiding them. She keeps them from escalating. I am struggling. I stay calm (I am a calm person in general) I don’t yell or get angry but don’t say the right things to my daughter. I feel like I say the right thing but she melts down and it takes 45 minutes for her to come back. I am feeling really lost. Any dads out there? Could really use the help.