You're not really a one hit wonder unless your career is over and you only had one successful song. A lot of people hated Call Me Maybe but it was still really popular and shes still making music, she could have a future song thats just as popular!
I wouldn't say so. Call Me Maybe was #1 on Billboard Hot 100 for a very long time. Tonight I'm Getting Over You was #8 on Billboard Hot 100 (which is a good place) and Good Time was placed #8 too. Her album Kiss was #9 on Billboard US and Curiosity was #6 on Canadian Charts. That's pretty good :)