V.W.
Use the natural consequences... It's the only way she'll learn. When I was younger I HATED having my hair brushed, mostly because my hair was uncontrollable and would get tangled literally 5 minutes after brushing it. So the rule became, over the summer I don't have to brush it if I don't want to but as soon as school started again it had to be brushed every day. Ya... That first summer I didn't brush my hair the ENTIRE summer. Then the night before the first day of school... Well, let's just say there were a lot of tears. The next summer, I brushed my hair every single day because I did NOT want to go through that again.
For the sunscreen, let her get burnt once or twice... She'll learn. If she doesn't, then start making her put it on again because you don't want her to develop skin cancer or something like that.
For the shower, let her go without... When school starts back up and every one starts making fun of her because of the way she smells, she'll get the idea and start taking showers again.
For the meals, stick with the rules... If she doesn't eat when you eat then she doesn't get to eat. Don't give her the snacks in between meals no matter how much she begs. After a couple of missed meals, she'll learn. I'm not sure if you guys are the type to all sit at the table to eat or if you guys are the type to scatter around the house and eat where ever is comfortable, but if you are the type to all sit at the table... Make her sit at the table with you and the rest of the family eat whether she is eating or not. She'll eventually get bored with just sitting there watching you guys eat and will join in.
For the bedtime, let her stay up as late as she wants. Keep waking her up early and don't let her take any naps during the day. After a couple of days, she'll be begging to go to sleep at a decent hour!