Is an only chicken ok?

I have never had chickens before although I've thought it would be neat. But now my reason for getting chickens is my horse. I need a companion for him other than a horse or pony because he goes crazy when he leaves them. So I thought of a goat but they are hard to confine. Then I remembered racehorses having chickens as mascots or companions to calm them. I only want to get one hen so she can bond with Trophy, my horse. I know this may sound crazy. The hen will also be a family pet so she will have lots of care and attention. My question is, will it be cruel to have her not be with other chickens? I thought to get a pullet around 3-5 months old because I don't want to get a chick and find out it's a rooster. Then, if it's a young hen, it can still bond with us and Trophy. I'm going to put the coop and run inside Trophy's stall, a two-sided covered area that's 14'x14'. I'll make it a tractor that can get out of the stall sometimes. The coop would be 2'x3' and 4' tall, with a 1'x1' nesting box inside, raised off the ground. The run would be 2'x8' and 6' tall. Is this an adequate size for a single chicken who would be confined about 3/4 of the time? I would let her out to free range for an hour or two every day. Thank you for any information you can give me.