In this case, it's a poem for kids that she first wrote (and had published) when she was just a kid herself - aged 12.
Hmmm, I don't think Jenny can claim it was professionally published back then. If I'm right about that, her first professional publication is still a poem in the magazine Dolly when she was 15 or 16. But I guess this will now be her first work to be eventually professionally published, or something. I'm not sure quite how she looks at it, but congratulations to her anyway!
Edit - come to think of it, the $5 Jenny got way back then might be quite respectable in modern terms if we adjusted for inflation!