I reached the barn, and she was standing in the barn aisle. The doors were only open about 3 feet, and the metal chain with the do not enter sign was still up - it's at about waist height. There was chestnut horse hair in some of the chain links. The gate to her paddock was lying on the ground, off the hinges. The chain across the aisle from the paddock was broken, and the rope was still up - these are also at about waist height. I went in the barn - she was good about haltering and I put her in her stall. I checked her as best I could for injuries - other than a few scrapes on her front legs, she seemed uninjured. She'd clearly been in the aisle for a long time - there were many piles of manure and all the hay bales were tossed around. From the location of most of the manure, she had spent most of her time in front of Charisma's stall - yesterday, she had briefly escaped from my daughter and made her way up to Charisma's paddock and had spent some time sniffing noses - Charisma is the one horse she knows.
In the stall, she did a lot of head-shaking, snapping of teeth and rolling - I think when she is anxious it makes her physically or emotionally uncomfortable, or both. She did settle down and ate her breakfast and hay. She will stay in the stall today and tonight, since at this point I'm not sure we can secure her in the paddock. For extra security, during the the day I have done some extra securing of the stall door, which a determined horse could take off the rolling hangers, and have also tied the barn doors shut. I think she'll be OK tonight when the other horses are inside - we wouldn't want to tie the barn doors shut at night for fire safety.
It's very sad - although up to this point she's showed little interest in the other horses, apparently she wanted to be with Charisma last night - perhaps Charisma reminded her of a horse she once knew. I feel very sorry for the horse - we've done and gone over everything we and our advisers can think of in terms of diet, medical, physical and training issues and we're left with no solutions to her serious problems. Thanks to all of you for your thoughtful comments.