Well, as the parent you know what's best for your child. You wouldn't let her eat ice cream and candy for every meal just because she wants to, so she shouldn't be able to dress in a way that's hazardous to her health just because she wants to either (we're not talking 50F weather). So I think you need to be more direct and matter of fact about it, "it's cold outside, put your coat on." If she throws a tantrum or sulks at you,ignore it. This is most likely a control issue. Let her make as many other choices as possible, such as choosing WHICH coat she wants to wear or which pants/leggings she wants to wear with her skirt.