Well, I believe that in both of these countries, tertiary education is held to a certain standard, so you're going to get a certain amount of quality in your education whichever country you go to. I'm currently based in the states though, so I'll say I'm more biased towards the states.

Honestly, I don't see why being a girl should affect your choice of engineering. Even if there are less girls in mechanical, it doesn't mean that you can't pursue it.

As for the cost of living, like what cagedbird has said, avoid the big cities. There are quite a few academic institutions based in small towns, and are basically college towns, which have a much lower cost of living than those in the big cities. But based upon personal opinion, I would say that California is generally an expensive state to stay in.

And for the 3.5 CGPA, if you desire that, you'd have to work for that, meaning, stay on top of your work, do the assigned readings, go talk to your professors and TA's for help if you need it. Professor's are generally rather open to being asked questions, and actually like it if you do so here (for the most part).

Oh, out of curiosity, why do you prefer Georgia Tech? Any other universities that you're planning on applying for?

I'd say that it's a very achievable goal actually.

Oh, and quite a lot of unis don't require interviews, except for ones like MIT. I didn't require one when I applied for unis in the states.

I'm guessing that you're going to be transferring in though? I'm not too sure about the procedures for that, I went to the states as a freshman.