Having also been blessed/cursed with a high
metabolism, I have only found *one* way that
works for gaining weight: a combination of
weight gain formula and a weightlifting
program. There isn't any other way. Just eating
a lot won't work, neither will just taking a
weight gain formula. You'll metabolize it all.
(Believe me, I've tried that.) If you eat a lot (or
take a weight gain supplement), and work out,
you'll put on some muscle, which is heavier
than fat.

Now what with you being a girl and all, I don't
know exactly how muscular you're wanting to
get, but if you're only wanting to gain 10-15 lbs,
your body shape will not change much at all.
Mine didn't. I'm fifteen pounds lighter than I
was when I played football, yet my body
shape/build has not changed at all. I've just
lost some muscle. If I put that 15 lbs back on,
you would not notice. I would think that if you
put on 10-15 lbs, it would not drastically alter
your shape.

So, in a nutshell, the suggestion is: lift *some*
weights (I'm not talking 2 hours a day, or
anything. Something like 30-45 minutes a day,
3 days a week, very basic lifts), and either eat
a lot more, or take a weight gain supplement
(those are expensive, though.)

The Other "Or you can start eating lead. I hear
that's dangerous, though" Matthew