scaredy chicken

i have an 10 month old beautiful std blk cochin hen named Ella. she was one of two hatched from my very first incubator attempt. she was raised up going back and forth from my daughters school (kindergarden class pet). she acted normally for about the first 3 months then i put all the chicks out into the larger coop. during this time we had a dog attack that killed a majored of the chicks including her brother. ever since then she will not leave any enclosure that i put her in. i have to force her out, and then she still will not leave the area around the door. she will not interact with the older chickens though she is a good broody. she raised 12 EE chicks that are still with her. she cowers in the corner if another chicken comes into her coop. her best friend is a large male white rabbit. she is very docile and friendly with people. she is just anti-social. she is very beautiful and i would like to breed her with my std blk roo. can any one explain this or offer help?