Hi Caroline
I'm an older person, but have played much sport all my life and dance competitively now. I've had lots of foot problems, so my advice to you is:
1)Find a really good physiotherapist - ask local sports teams who they use, or ask around - to assess your whole movement.
2)The problem may not be coming from your feet - it may be posture related, the physio will be able to sort that out
3)As Laura says, any remedial treatment will take time, though knowing you have a solution will improve your motivation greatly, and a year could see great improvement
4)Yes - people do wear orthotics while dancing. Get some good practice shoes. All my little niggling foot problems disappeared when i bought some practice shoes from Supadance (by the way - thanks Supadance, if you're reading this). If you need orthotics, the physio will tell you
5)If you're given strengthening exercises or flexibility exercises to do, make sure you DO THEM. I know this sounds silly, but i have friends who get advice from a physio and ignore it.
6)Keep dancing!!