It's OK to get upset when you talk to your child as long as you explain you're upset at the behavior and not at them. As for the meltdowns, I like to use natural consequences. If she doesn't want you to untangle her hair let her go to school that way. I'm sure a day or two of her peers teasing her will quickly change her mind about the merits of brushing. It would be helpful for you to pick up a book on positive parenting. Instead of you punishing your child for their behavior they are choosing their own consequences. If she doesn't want her hair brushed she will have to walk around looking ridiculous and getting teased. If she doesn't want to clean her room, she won't get to participate in the fun family activity and so forth.