13 month old naps

I have a 13 month old little girl. She has been refusing her afternoon nap for about a week. I thought she was working on dropping a nap but she is exhausted by 9am every day and if I try to push her nap back she loses it. I have been taking her upstairs and trying for a second nap each day but she usually just nurses and relaxes for an hour without sleeping. Should I keep trying for a second nap or push harder to drop one? I'm not sure if this is a phase.