I want to learn to play a musical instrument for classical music.Which one should I choose?

I always thought of myself as someone who could not do that but now I am ready and so willing to learn to play! My goal is to eventually play in a local band of volunteers. I want an instrument that is more suitable for a girl and that is not too hard to learn. I will appreciate any insights:)

No offense, but by "an instrument suitable for girls" (and "not hard to learn") you are already limiting yourself. "suitable" instruments are "not hard to learn". It's the developing skill level, not the learning, which is difficult.

I've been playing instruments like trombone, trumpet, and french horn for five years now, and I get crap for being a girl all the time. But to hell with that. I can play three instruments vey well. So girls can play anything.

If you are going to settle into stereotypical roles, then you don't need to be playing an instrument.

I am not sure what the significance of you being a girl makes.
It really is not a question of an instrument being difficult - that really is a function of the music that you intend to play. If you are going to play simple music, then most instruments will be relatively easy. If you intend to play violin concerti - then that is a different matter. It is largely a matter of commitment and work ethic.
Which ever instrument you choose there will be an element of hard work.
Like most other things - you extract in measure what you put in.

i say go for the violin. i started playing in 4th grade and its pretty easy. and if you want to make a transition into guitar (which i did) it makes learning guitar alot easier.

Well, if you are aiming for anything that is not a stringed intrument, it depends on the way you mouth is shaped some times.

I play flute, but I know that some people can't play it because they have teardropped lips or something like that. The flute is fun, so it the sax. Don't play clarinet, it's not any fun. Oboe is fun, but hard. So is basson. Percussion is fun but you have to focus.

It depends on what the band needs. You should ask the band director if he needs French Horn or Alto Saxophone or whatever you think you would like to play. I taught beginning band in the Oklahoma Public Schools and those were instruments that most high school marching bands need. I happen to play the French Horn so that would be my first choice for a young lady.

Instruments are gender neutral. Your being a girl has nothing to do with your choice of instrument.
All instruments require hard work before you sound good. The kazoo is probably the exception to this rule.
I would choose the violin ; difficult, but the most beautiful.

Unfortunately there is NO instrument that is not "hard to play," particulary in the classical/symphonic arena.

Given that, Violin is among the very best choices. They are virtually always present in the classical genre. And note that the Orchestral Concert Master is virtually always the first violinist.

Viola and Cello, might very well be good 2nd. and 3rd. choices.

definitely go for either the bass or tuba either would be perfectly suitable for a girl.

pick the one YOU want to play otherwise you won't want to practice .... as far as opportunities ... viola 1st then cello would give you more opportunities to play in a community group