I have two girls and a boy--my oldest and my middle child, my son, are 17 mos. apart. Of course, since my oldest was first, and around longer, she wore girly, frilly things for her first 2.5 years of life, had all girl toys, etc. After my son was old enough to graduate from baby toys to boy toys appropriate for his age, my daughter began liking alot of his toys, and soon, anytime I bought either of them anything, I had to buy the other the same thing, and this went on for years. In fact, she is still, to this day, not very "girly," whatever that is supposed to entail. She is feminine enough that everyone knows she's a girl, but not into pink, or "froo-froo" anything, not a girly-girl at all.
My youngest, a daughter, is totally girly, pink's her favorite color, and all kinds of into the cute and cuddly, frilly, dresses, and all that.
I will go with the default response and say that all kids are different in one way or another, even if they're the same gender, and she will be different than the boys, no matter what. Also, she's the "baby," and the only girl--of course, there will be differences inherent in that situation. Not to mention, father's do treat their daughters differently than their sons. My husband is proof.
I am sure that if you continue to treat the boys the same as you always have, and your baby girl garners her own special kind of treatment, things will be fine.
Congratulations!
KW