Hi Jennie. A flying saucer wheel can be nice as an extra in a cage if you have space, but they do need an upright wheel as the main wheel as the others say
Also a flying saucer for a Syrian needs to be a 12" one. I am a big fan of the 12" Silent Runner and did a video review of it
It's not a cheap wheel at approx £25 and I also paid an additional £5 for cage mounting plates, but it's the best wheel I've had and been using it for a year with no problems whatsoever.
https://www.youtube.com/watch?v=VFussTX5PuE
Sounds like your hammy would be best settled in the one cage with a conventional wheel from now. She is maybe a bit young to get the hang of a flying saucer even as an extra.