My daughter bought her game used and opened a new file named after herself and has been working on her town. The game is new to us and we did not realize the previous owners info and town still exists. Is he the mayor? Is there anyway to delete his file without damaging hers. Will she then be the mayor. Thanks. I am not a gamer and she is just starting so any info would be so appreciated.
You should really check that there is no existing data from another user, when buying a preowned game. Unfortunately, I do not think it is possible to reset the game and keep her progress without a second 3DS system and copy of the game.
If you do have these, then it is possible to transfer non-mayor players to fresh new leaf game cards. I found a YouTube video on how to do this for you.
If you don't have another 3DS and game card, then you will need to deleate all data. This will mean your daughter will have to start fresh, but she should have a bit of experience on how to play. Here is a video on how to do that: