Clothes in bed? That's strange. Just pull her close and tell her you'll keep her warm.
That's not gonna work baby! You gotta find out what the real issue is.
* Do you need to turn up the heat in the house at night (energy efficient or not) or get her a dual control electric blanket. If she's cold she's wearing sweats to bed.
* Is she uncomfortable sleeping naked and now that you're together all the time and she's used to you she feels like she can sleep the way she really wants to sleep - clothed.
* Is there an issue in the relationship that she's trying to avoid intimacy? Are you spending quality time with her outside of the bedroom? Do you listen to her? Do you know how she's feeling emotionally right now about the relationship?
* Have you been an asshole lately and she's just cut you off for the winter?
Contrary to every man's desire, a lot of women actually sleep better with something on... old t-shirt, night shirt, night gown, pj's. We all have our favorite thing. There are some families that don't believe in sleeping naked and even though she's an adult, she may honestly feel more comfortable being dressed when she comes to bed. I know some girls like the feeling of having clothing removed too, but that is more rare.
It might be that you just need to actually, oh, I don't know TALK TO HER ABOUT IT.
Just a little advice from a girl that likes to sleep in a slip. I like the way it feels on my skin. Used to sleep in big white men's tshirts. My shoulders also have to be covered by the blankets, even in the Arizona summer heat... at least a sheet over my shoulder of I can't sleep.