Greetings and welcome to BYC from NE TX! So glad you joined us. I hope you'll consider taking a minute to visit the new member's thread and introduce yourself so folks can welcome you properly.
https://www.backyardchickens.com/forums/new-member-introductions.44/ It could be any number of possible issues that make her want to stay outside. Maybe too hot inside, possibly lack of adequate ventilation, poss too crowded on/off the roosts and she's being picked on. Short of locking her inside the coop for up to a week so she learns that's "home", there's little you can do if she doesn't want to go in on her own.
Just as an aside, you said the coop has 30 sqft... and you have a dozen birds... Coop square footage is best at 4sqft/bird (or more) of open floor space for large fowl (LF) birds. You speak of a BR so not sure if the rest are LF's or bantams. Bantams can do with less space of course. Also, you should have 12"+ (18" is far better if it gets hot where you are) of roost space per bird. Chickens wear down jackets year round and generate a LOT of heat. Think self heating sardines, packed in a can.
There's a wealth of info, knowledge and experience shared in the multitude of threads. Browse around and see what interesting stuff you can find. By all means post away when the desire strikes you, especially if you have questions (provide as much detail/info as possible and pictures truly help)... With all the great folks here, generally someone will respond in no time at all. Please make yourself at home!
PLEASE put at least your general location in your profile. It could be very important if/when you ask for or offer help or advice. You know, climate issues and such. I recommend at least your state as most folks won't be able to figure out where if you put anything more specific (county, town, street, etc) by itself. Old folks like me will never remember & look there first. To add it, mouse hover over Account top right and a drop down will appear. Click on Personal Details and scan down. You'll see the spot for Location. Then go to the bottom and save changes. Thanks! Hope you enjoy the site!