Can only play Minecraft demo?

I bought a minecraft account and played with it for awhile. Then I wanted to give the account to my sister. I changed email to hers, password to her choice and now I want it back. She can't play because it says it was registered under a different email. We switched email back but it still only lets her play demo. Ideas? Maybe the bought version is still on the old email. Try and contact Mojang for help if you are 100% sure that both emails are no longer linked to the premium version that you bought. What do you mean by only lets her play demo. Like can you log in to the account or not?

What do you mean by only lets her play demo. Like can you log in to the account or not?