A friend of mine had scoliosis that began to develop shortly after the onset of puberty. My understanding of it was that he was growing at such a high rate that his spine wasn't able to take on the extra weight and the muscles stretched so tight that they pulled his spine sideways fast thus causing the curvature. It was caught early
enough that he was able to "fix" it by wearing a brace which straightened his spine over time (two years).
While I do think that diet can help to prevent things like bone loss and some developmental disorders, I find it unlikely that you'll be able to straighten your spine with diet alone. You may be able to strengthen your spine but without a physical support, I don't see how the bones would find their proper alignment on their own. If you were to break a bone, then it would need to be set in the proper place then held in that position with a cast or metal splints/pins while the bone healed. Certainly a calcium rich diet would go along way in aiding the healing process, but unless the bone is in the right position all you'll accomplish is a healed crooked bone.
My brother was in a really bad accident in his early 30's which caused him to be in the ICU for 6 weeks before he was stable enough to be operated on to fix broken bones. by the time the doctors opened him up his leg, thigh and hip had already begun to heal in improper places. The surgeons had to re-break the bones in order to get them in the right positions to heal properly. The bone in his hip was so badly broken that the doctors said it looked like a bowl of corn flakes (hundreds of small pieces of bone), though by the time they got in there most of them has begun to heal in that messed up form. Bones don't know where they ought to be, they only know where they are. If they are broken or misshaped, they heal in that form.
If you are really interested in fixing the shape of your spine you'll likely need a physical intervention of some sort. That might mean a brace or surgery to remedy the alignment, then focus on the diet to improve the healing process and prevent further damage. Sorry if that's not the answer you're looking for but it seems only logical to me.