Is it fair for my stepmom to treat me like this?

My stepmom was just pregnant and she gained a bit of weight so I thinks he might be jealous. I'm 15. I want to wear a skirt. God forbid. I don't want to look like a skank. But when it's blazing hot outside I don't expect to wear tights. She was yelling at me to wear tights the other day under my skirt. It's one of the pencil skirts. All I was doing was going to the mall with my friends. Then a week ago I wore shorts that aren't below my and there normal. She stopped me and told me to put on longer shorts. And you gotta keep in mind I am from Florida. I'm dressing like a normal human being would on a hot day and she's yelling at me to cover up. Also throughout the year she always yells at me to wear a shaw or a cardigan over a tank top. It's so annoying but yeah my question is.. is it fair?