Hey ToKiss -
Are you a small person naturally? What I mean is that a size 2 is tiny, tiny, tiny - Is that a reasonable expectation for your body frame?
I am a large-framed person. I have broad shoulders and hips and know that my body would probably never be smaller than a size 10 just because of how I'm built and how I carry my weight. (big boobs and ass - SHAZAAM!)
I encourage you to give yourself reasonable time to be the size you want - Or hell, don't even focus on the size but rather what makes you feel good.
And I'll tell you something else - I am hearing you say that dressage is important to you and you want to be "seen" in the ring. I say fuck the idea that fat girls are out of place! Who made that rule? Who says that fat girls, or medium girls, or girls with small frames aren't all deserving of being in that ring if they've worked hard for it! I think you should get in that ring no matter what size you are and show those people how a fat girl works it.
Don't let someone else's idea of beauty control what you do! If you want to be in that ring, get in there - No matter your size! (and not in spite of your size, but BECAUSE of your size.)
You are perfect just the way you are. I think it's totally ok to want to be healthier, but do it for YOU!