Can't log in with existing account

I bought my friend minecraft around a year ago or so, can't remember how long ago it was, but no longer than 2 years ago.
She created her account and played for a while, but then played other games and forgot about minecraft.
Me and my boyfriend bought a realm to play in, and wanted her to join us, so we sent an invitation to her, remembering that her nickname was "Envye".
She tried to log in in her computer but it didn't work. I thought she might have the old starter, and needed to download the new one, so she tried to log in my computer instead. It didn't work. I asked if she had the right password, and we changed it just to be sure using her email. She changed it, and tried to log in using both, her nickname and her email. Neither worked. We don't know what the problem is, and she can't log into her mojang account either. But her email has been used, and i remember paying to buy her minecraft. Well, my boyfriend used his card, but i gave him the cash. My friends email is: petra.koskela@windowslive.com