cover art source: http://adailey.deviantart.com/art/Watching-316189762%0A
Queen Chrysalis' plan to invade Equestria was not only due to provide sustenance to her subjects but also a form of revenge towards a certain Captain. It includes the attempt to marry Shining Armor even if it means sharing the same roof with a pony and not to mention stealing him from his love.
Before Shining Armor became Captain of the Royal Guards, he met a certain creature during one of this guard duties. he soon found himself befriending this creature let alone have feelings for her.
Before she became the evil queen that tried to invade Equestria, Chysalis was no more than a young successor to the queenship of the changelings. Being separated from her people, she soon wanders off to a town and met a certain unicorn which will change her entire view on what is 'love'