Originally Posted by scottyfox
Well, I don't have much in the way of advice, other than be ready for a bunch of pervy guys staring at her, except to say with a BMI at around 16, your girlfriend needs to put on some weight!
At the field that i play at (private Waterdown area field) there are a few ladies that have shown up with their lesser-halves - and no one has perved out on them in the least. The girls, once the equipment is donned, are nothing more than another set of boots on the ground, enjoying the sport alongside of their partners, just as much as the guys are. The closest thing to staring being done, is through a telescopic sight, along with the generalized thought process of "i wonder if i can hit that player, from here".
To the OP - find a field with generally mature players, more serious about the sport, and generally less inclined to be ogling the competition, male or female. They are out there.
As far as the weapon package goes - yes, an MP5 should be a good fit - but there is no reason why any other CQB'ish length weapon platform couldn't be considered. As it goes with the guys, so too it goes with the girls - it's more about personal preference, than physical ability to handle it, with any half-ways physically fit individual. Get to a shop, and try some guns on for both heft and ergonomic preference.
As for vest/chest-rig/plate carrier, again, it comes down to finding a selection at a brick and mortar store, and finding out what would work for her.