you say that you have trouble talking with her right? well how about this, pick a place you feel comfortable, like a coffee shop, or your favourite restaurant, take her there and say that we need to talk sister to sister about some things. once you break thee ice with talking about normal stuff like thee weekend or whats on tv, try easing your way into thee conversation about you and her's relationship and how she treats you.
if thee way she's treating you really bothers you that much, then tell her. not in a mean way though, say something like "i know you want to protect me, and i know that you're older, wiser, and more experienced than me, but i think that thee way you are treating me like a child, is just kind of difficult for me because i want to be myself around you, and i can't be because of that."
she's your big sister, and she's going to treat you like a little kid, its what big sisters do! thats what my sister does

but get your voice out, let it be heard by her, and even if nothing changes, at least you know she heard your point of view on thee way she treats you
