if he's ok with doing this now, god knows what he can do when they are married. He wasn't angry at the burnt food. It's not normal to throw food in someone's face if they didn't make it well. People do this when they are having a bad day, and when something else goes wrong, it's the last straw and they take it out on whoever they feel they are superior to. This is very dangerous behavior and a huge warning sign of domestic abuse. YOu should tell her that forget the preparations and don't think about all work everyone has done so far- and seriously think about whether she can handle this. a few months of wedding prep is insignificant compared to a life of abuse. Initially, everyone is 'lovely'- but when problems arise- this is where some people's ugly sides come out, and they may be very ugly indeed. She must learn more about whether this was a one time thing, or a joke, or if these are his true colors, and he should take anger management class or psych evaluation/therapy if she still wants to go through with it.
He obviously has no respect for her if he feels like he can throw food in her face. She should have done it back right then and there- it would have shown him that he can't treat her like that. What are her parents saying about this?