It depends on how hard you are willing to work. Getting a six pack is notoriously hard for women to achieve but not impossible - and individual genetics comes into play here too...easier for some women, harder for others. YOU CANNOT SPOT REDUCE FAT FROM THE BODY THROUGH SPECIFIC EXERCISES. \I cannot stress that enough - no amount of sit ups (which are for the most part highly ineffective and a waste of most people's time unless you're doing it correctly and even then there are far better exercises for toning the transverse, rectus and oblique muscles)
The single biggest thing you can do for your six pack is diet - around 80% of what your body is composed of is DIET. A clean, 5-6 small meals a day, moderate (good) fats, low(ish) carbs, high protein, plenty of veg (fruit stick to just ttwo portions a day those being berries and melon and only half a cup of each = 2 portions)
The second most influential thing you can do for that 6 pack is lift weights - and I mean LIFT weights, not fannying around with a couple of 3lb dumbells doing 3 sets of 15 reps (what a complete waste of time). Muscle burns calories, builds bones, protects the body from injury, improves stamina, strength, energy levels and balance/coordination. Will you start to look like a man? Yes - if you supplement with illegal drugs, live in the gym and supplement even more with illegal drugs. If you lift properly, decently and regularly you will improve your BMR (basal metabolic rate - meaning more calories burnt even when you sleep) and your body shape.
You have a very small amount of time to achieve body fat loss and muscle gain. I have no idea of your basic genetic make up (accounts for about 10% of how you look) or your current body fat % (and it's body fat % that dictates the appearance of a 6 pack) - but even starting in relatively decent shape you will have to work hard.
I used to lift, I'm just an amateur, but I used to work bloody hard and never achieved a 6 pack (did have a decent vertical line though) because I never got my body fat low enough - and I'd never try to keep my body fat so low as to have a 6 pack because for most women that would be unhealthy.
The best resource I used to use was Oxygen magazine - great tips, great diet advice, great workouts. If you see women in there truly muscled up don't wory - they are at their competition stage - ripped to shreds - it's not something they sustain al year round and most of the year they just look pretty good - and to even get to look like them when they are not competing you have to work extremely hard.
I also used to use the Spartacus workout.
Both of those can be found in a google search
HTH.