Low body fat %
So plate push aways are the best option
There are several factors that affect whether you can develop a six pack. First is genetics - some people just won't develop those muscles the same way others will. Another is the % of body fat - you can have these muscles but they could be covered by a layer of bodyfat. Unfortunately for a lot of us, that layer won't come off unless we are on a very strict calorie reduction diet.
That all said, in your case, you are doing very little strength training. For women to develop definition, we need to eat more protein (as was mentioned) and lift heavier weights. I recommend Starting Strength by Mark Rippetoe. This is a 3 day a week routine, and you will immediately start to put on muscle. The SS program is based on full body exercises, so you don't have to 'spot train'. The natural pushing will build strength all over, including your abs. Just doing barbell squats will help with ab definition. Trust me - you will not get bulky, despite what other people think about women lifting. You don't have enough testosterone for that.
As a vegan, you'll need to find ways of getting protein into your diet, as this builds muscle. If you are not a strict vegan and are open to dairy, these foods could be helpful. A lot of guys who lift drink a lot of milk to get it. You could also look into whey protein.
Hope this helps!
Diet, diet, diet. You can have the strongest abs in the world but if you don't have a low enough bf % then you won't ever have that '6-pack look'. You also need to make sure to get enough protein, as previously mentioned.
Also, as with any other muscle, there are exercises that work better than others. There IS a "right a.k.a best" way to work on your core. Doing things like sit ups for 5 minutes is not one of them (not saying that's what you do, just things I've seen/read before). Treat the abs like any other muscle group in your body. Stay away from flexing motions that stress your back and don't target your abs as well.
Squats/deadlifts (not on a smith machine) will do wonders for your core.
I was able to get a 6 pack with just pilates and tangential weight lifting (i.e. it wasn't really my focus) HOWEVER, diet and low bf % is what really made them pop.
I followed a 90 day routine + meal plan. LOTS of protein and vegetables, minimal carbs (i.e. only eaten as a quick energy source). It was tough, and the meal plan was kinda similar to a pre-competition body builders diet. Truth be told the diet was very boring, but it did the trick. at the end of the 90 days I was incredibly lean and 6-packy, and my bf% was in the mid to upper teens.
It should be noted that the diet is probably not sustainable for the average person. I set a plan for 90 days and achieved it, yet I know I wouldn't be able to continue the plan past 90 days without losing my mind from the sheer monotony of it all. I still have a 4 pack which is maintained through average* eating and average* working out. Personally I feel like 6 pack abs, on females, is an ephemeral goal as they only appear from a low bf % and a restrictive diet that is difficult to maintain naturally.
I feel like if you aren't getting paid for it, there's no need to strive for it, as 6 pack abs easily disappear because of 1 too many slices of bread.
For what it's worth, I don't think most males find females with 6 packs very attractive either.
But you may not give a ** about that.
Most of the major points have been touched upon in the replies above, the most important being body fat. Everything I have read on the subject mentions that if your core muscles are strong you need to do a great deal of cardio to cut your body fat (which appears you already do). I'm just happy to have my one-pack, or keg, as it is called, but seriously, my abs at the top are defined but I have bodyfat around my belly that keeps my lower abs from popping. My problem is I eat too much at times and undo all the weight I have lost over the course of the week. If you can cut your body fat you will see your abdominals get defined. If that doesn't work, join the masses of people who have accepted that they will never have ripped abs, no matter how many ab machines we buy from the late night paid TV ads. I hear those air brush guys can do wonders for painting abs on your body. Just sayin'.
^^^ those machines don't work. they're a lie. just like those raspberry ketone things for losing weight.
OP is almost 17, 5'11" and weighs btwn 127-130. She dances 4-6 hours per day, 6 days per week. She eats a diet of mostly fruits and veg (she's vegan) -- I somehow doubt she has anything more to diet off... And rather than pushing away from the table, she should actually be getting a step or two closer.
the answer is SIMPLE. its your diet. you can do crunches, sit-ups or whatever else all day long but if your body fat% is high you will not see abs. Maintain a healthy diet along with tons and tons of water.