I can play either character in the following...
Sister/Sister Sort Of A 24yo female is living in LA trying to make a go of modeling/acting and having moderate success. Her younger sister [16yo] comes out to visit for a summer. The last time the older sister saw her younger sibling a few years back she was a tomboy. There have been changes. Tho sexually still a girl her younger sister looks all boy. Those who don't know her assume she is a boy without a second look. The younger sister is the more dom of the two.