Sophie Turner will hurt her career
I can easily see Deborah being considered for Sansa in GoT or Jean Grey in the upcoming X-Men film (Daredevil isn't as high profile) but both parts went to Turner. Deborah is 11 years older and yet has a rather poor track record as far as her film choices goes whereas the younger Turner is making better choices and is proving herself as a leading lady in films (something Deborah has yet to do).
Both are very similar and would go for equally similar roles yet as far as acting goes I've yet to see anything remarkable from Deborah; while Turner isn't great either she is only starting and has shown some good stuff in GoT. In terms of beauty I think they are very much on par.
I definitely see Deborah losing some good roles to Turner further down the road.