Do you have many kids in your area dying of hypothermia? Or exposure?
I only ask this bec you sound like a very caring parent, but you don’t seem to trust your child to come in from the cold when she’s cold.
If she doesn’t have any pain receptors to extreme cold I’d be asking a specialist why not, if she’s coming in with second or third degree frostbite.
So my next really hard question is why is this such a sticking point for you? Do you feel like a bad parent or lacking parental skills, because it sounds like you care very much about her health.
I must admit 6 yrs ago I was very pregnant & we had a huge snowfall & my girls were driving me crazy! They wanted to go outside naked in the snowstorm. Really! So my SO put their boots on & they went out naked! Made a couple snow angels & ran back in. They were exhilarated, but also knew that cold can hurt.
And I do understand very well about being an overprotective parent. 9 yrs ago we lost our 23 month old niece to a very preventable household accident. It changed us significantly & how we parent. I learned to take some deep breaths & stand by my parenting pillars, but also how to compromise.
So if she wanted to go outside in a t shirt, which is just over the top, maybe compromise (& explain the word to her) & say well how about not a t shirt, but a jacket would be great.
Deep breaths! And enjoy the compromises bec she’ll learn to trust you more & know you’re will to negotiate instead of a flat out no. It gives you wiggle room to say YES!