You need to feel her leg up and down for lumps, cuts or swelling and heat to determine if it is her leg or foot giving her the trouble. Lift the hoof if she will let you and gently pick and brush it out to see if there is a rock or some other object imbedded in there causing pain. She could have twisted it or pulled something tripping over the frozen ground or been kicked by a pasture buddy. If the footing in her paddock is frozen and uneven then you should put her in, as hobbling around on uneven footing won't help matters. Many horses get sore footed on this type of ground, especially after recently being trimmed. In a large pasture, they can avoid walking on it and you can help by moving feed and water away from it so she can walk on smooth ground. In a small paddock, this is hard to avoid, especially with several horses in there. I do not think she will be able to rest in the paddock with turn out buddies in with her. On another note, Unless she is in lush pastures, she needs hay every day, or some sort of hay substitute at least. Sunday is a too far away to go without food. I would stall her because of her lameness, and go buy a bale from the feed store if you have to, even buy one off a neighbor or something. Lame horses need rest to recover. If she does not improve in a few days you need to call a vet to get some pain drugs to prevent her from suffering, especially if you cannot find any source for the lameness like a cut or bump.