I love it. I had a cat called
Jemima back in Australia, and named her that partly because I thought the association with the doll in the Australian kids’ TV show Play School would be too strong to use it for a child. Here in the UK it’s been steadily popular for a couple of decades, though, and I could see myself using it despite having already used it for a cat once lol.
I would use
Jem as a nickname.
https://nanowrimo.org/participants/christine-seaforth-finch
http://christineseaforthfinch.blogspot.com/