No and nothing. Running with weight is a guaranteed way to get an enduring lower limb injury.
We throw ourselves around the place operationally carrying significant weight, but only - hopefully - after aquiring the necessary strength and stamina through a progressive training programme.
The key to this is cross training - don't just run - cycle, swim and beast your legs on the weight machines in the gym - or do plyometrics (squats, squat-thrusts, leg raises) and isometrics/pilates exercises if gym membership is an issue. Do NOT NOT NOT run with weight until you need to. Dno't get me wrong - the Infantry 2 miler is where you want to be (2 miles at best effort with 55lbs of kit - bogey time 18 minutes, but I;ve had a CSM and a PL Comd who did it in 12 mins. The freaks.)
The safest, most time efficient way is probably free weights (dumb bells and the like) especially if you can get good coaching. That said they will develop what strength you need as long as you can make the entry requirements. I'd recommend the pilates route as it will stand you in good stead in terms of injury prevention later on.
Edited to add emphasis where it was needed.
Edited again to add yet more emphasis where it was needed.
When you arrive at AFC they will be expecting exactly that - a 15 year old girl, not Arnie
Get out and do some running by all means but the Army will see that you get strong mate and if you knack yourself with half-baked ideas before your start date - guess who won't be starting at all mucker.