When Im old enough I am hopping to become a horse trainer and maybe just hopefully my answer will help you. ( I have my own way of doing thing, most work! )
Well first make sure your horse is relaxed before going into the stabbles. (Massaging)
Then hold a bag of horse treats and crunch the bag, give one treat to her. Then get a friend to hold your horse infront of the stables, while you put your horses favourite treats in it's feeding bucket. Let her see your doing this! Once she has the idea she isn't going to get those goodies unless she goes in, she will then eventually walk. Make sure to not make her go in. For encouragement you must stay in the stables and encourage her to come in, while your friend hold the horse. ( your friend must let the horse feel free and let the horse be incontrol at this moment. So don't hold her so fermly)
Once your horse has gone in and finished the treats, leave her their for 5 minutes Alone! Then go back in and take her out of her stables and give her something else to do, like going out for a ride.
Repeat this 3 times a day.
Once you think she is understanding do the same but only do it twice a day and then do a little extra in the third time...Once she has finished her treat's give her a groom or get a horse massager in. Make sure she feels relax, it's best to give her hay or something to eat while your doing this. Only groom her/massage her for 30 minutes then leave her Alone in her stables again for 10-20 minutes.
As you may have guessed it is a slow prosess but its the kindest way to do. Once her 10-20 minutes is up do something that will take her mind off it, like if she likes to jump give her a jumping lesson.
Once you see a improvement in how she behaves in a stable slowly start decreasing the time you groom her I would do it by 5 minutes every two day. So instead of being in the stable with you for 30 minutes and 10 minutes alone she'd be with you for 25 minutes and 15 on her own. Keep changing and adding.
But make sure to still groom her in her stables at least once a day, and spend time with her in the stables. The best thing to do is put her mind off being in the stables. Give her something to do or watch.
I hope this helps ofcourse it is a slow prosess but who said horses are easy to look after, its all about trust and making sure your horse understands that you are not putting her their for her to be stressed, but for her to relax.
Also, do you know why she is not happy their? Is she happy in other stables? Maybe she is feeling uneasy because she senses something or isn't happy with her neighbour. Some horse dont even like the surroundings. Maybe its to noisy or maybe to quite. Try and make it that its just like old times and not to diffrent!