Trouble resetting Apple ID password

hi,

I got my mom a Iphone 6 and created different Apple ID to use for her phone. For her convenience, no passcode is setup. After about 6 months of use without issue, today her phone suddenly is locked and asked for passcode to use it. Of course no password I try is correct one. After verifying that one can use iCloud to enable passcode on device that has no passcode, I thought someone might have used this method to lock my mom's phone and it seems to be true because I can't access to that iCloud account anymore. When trying to reset that icloud account password, I am presented with this information:

Select how you want to reset your password:

Choose from the options below to reset the password for myemailaddress@gmail.com