and why they keep topher around

Doll personalities are created by "mapping" real people's brains, but there are also a lot of fictional elements as well. (If all that was in their brains was the original person's personality, they wouldn't be loyal to the Dollhouse or focused on the mission at hand -- or be caused to fall in love with whomever the Dollhouse feels like, for that matter.) Topher's genius is in blending one or more personalities with these fictional elements to make a coherent whole personality that does exactly what he wants. So instead of taking the abused girl's brain and "growing her up" into a functional adult version, maybe he took a brilliant child psychologist and inserted a past that included all the horrors that they knew the girl went through. It wouldn't be a perfect match, but it would be enough to allow Echo to bond with the girl and seem to know what she was thinking.