Early Bird or Night Owl

I think most parents who have two (or more) children will agree with the following statement.
One child is an Early Bird and the other is a Night Owl.
Anna is our Night Owl. She has no problem going down for nap, bedtime on the other hand.... well lets just say she has a frequent "get out of bed" card that is full every night. Why? why does she stay in bed for nap and not for bedtime.
Ben on the other hand is my Early Bird. His head hits the pillow and he's out (usually one of the times Anna gets out of bed she is checking on Ben; then proceeds to find me to say "Ben, sleeping.")
I think both children are connected, if one gets up in the middle of the night the other will within 1/2 hour. And they are both zombies for about 10 minutes after getting up, then off they go like our life is a marathon.
Any helpful hints with Anna's bedtime?