Thank you all for your help,
As she came into season this spring and we wanted to have a litter from her, I just thought I had to breed from her that year because of the jill's not coming out of season I just presumed that she wouldn't come into season until she was old enough to breed!
Could this be why she didn't catch with my hob and the more experienced ferret just sees her as a kit?
I have separated them now and it looks like she is coming out of season, will be ok for her remain entire until next spring? I'd love to breed from her but I don't want to put her health at risk.