wow! you do have a predicament dont you :)
based on a horse i had a few years ago i would venture to say that being stalled may possibly be a problem. when i was working at the equestrian centre i was riding this tb called taco. he was stalled every night and a lot of days because he could not have rugs on and the nights got down to about -4C and the days hovered around 10C. when i started riding him he had been stalled like this ever since he got there which had been about 14 months.
one morning i went to bring him to the arena and he was all sweaty and on edge. he backed himself into a corner and snorted when i went in and then pushed past me and bolted out of the barn. i went and got him and saddled him up and had my lesson and he was so naughty it was like someone had switched him with another horse.
he got worse and worse until one day he reared at me when i was trying to put him in his stall.
we decided to look back over the surveillance tapes for the last month (this was a verrrrrry expensive establishment and they had thought of everything right down to camera surveillance to protect some of the highly expensive horses there). it took me a long time to watch them all but nothing out of the ordinary happened.
someone made the suggestion that he was annoyed with being in the stall. i thought that couldnt be possible because he had been in there for ages with no problems. i was sure something had happened in his stall to make him scared and it was transferring through to bad behaviour when out of his stall.
when it warmed up a little i reluctantly put him in a paddock for a night. no change for the first week. i was so disappointed. we had a huge show coming up where points i earnt went towards my instructors certification and i couldnt even halter him in his paddock.
but i persisted and then one morning he was great. i went in, haltered him and bought him into the barn where i fed him and saddled him up. he was just like his normal self apart from being a tad more jumpy than usual but that even passed in time.
to get rid of the last of the sillies we did some desensitisation work with him. even though he was pretty bomb proof before he had developed some 'habits' i will call them, while he was all 'stall cranky' as i call it
as long as i left him in his paddock at night he was fine. i guess eventually he decided he hated the stall and would do anything not to be there...even lash out at me.
i have no idea if this is vegas problem but i just thought i would throw that story in :)
good luck with her