I am 5'5 and am skinny
I suggest you go with a Condor Chest Panel (
http://www.surpluspontrouge.com/en/h...t-panel/black/) if you are looking at a chest rig.
I myself am looking at getting one as my current vest is getting quite heavy to carry around and I want something light and more maneuverable.
My current vest is a Condor Compact Plate Carrier which had to be modded alittle in order to fit my skinny stature
Even then though it is a pain to carry around.
I did however use this following vest (
http://albertaairsoft.com/store/prod...id_product=568) for my first game and with alittle adjustment to the vest it fit like a charm. If you want a vest over a chest rig I suggest this. This vest I used was actually a friend's of mine who let his GF use. She is pretty much the same build as you, maybe smaller, so I know forsure it will fit you with the propper adjustments.
Might I suggest you get in contact with the user Barbie. She is probably a wiz when it comes to tac gear for women, and could recommend the best option to you.