I'm just giving you my opinion on locking her up. I wouldn't. There's a reason most horses won't stay in a shelter and end up staying out in the elements. She feels trapped as a prey animal if she is confined. A horse knows where comfort is and will congregate there. Being outside is safe for her in her mind.
If she becomes lame to the point of not wanting to walk or being able to get to water or food then that is call for putting her in. But, again, she may go nutty being confined. Attitude can change. And as far off as spring is she will still have to walk on that hard ground.
Just my thoughts and opinion. But you know her more than anyone!
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