Any time she isn't in dance shoes, put her in good tennis shoes with the supports. My son had Sever's disease on the right side--- he was in Nike tennis shoes constantly and we thought they were good on him. Nope. Changed shoes to a cushiony soled one and it helped.
Fast forward two years and he developed Osgood Schlatters too. Had MRI's, CT scans, you name it we did it. Changed shoes to Brooks (cost about $150- on a still growing foot, ouch) and it's much better but still painful.
Both can last for years. Rest, ice, elevate when at all possible.
My son is extremely active---- hates to be inside. Trying out for the HS soccer team tomorrow. His problems developed when he grew 6 inches in 6 months. Most of it in his legs, and his foot grew just as fast to keep pace.
Unfortunately rest and time are the only things that help these two problems.
Good luck-- it's hard to see your child in pain and have to limit their activities.