Thanks guys - I rang the on call vet and she said to try to get her to
take some cooking oil to
try and make it pass through her. I tried adding some oil to
her food but she wouldn't eat it, so I've been giving her "Defurrums" - they're designed to help them pass hairballs, so I figured it would work for this. So far, she hasn't passed it, but she's not in any pain or anything, so hopefully everything will be fine.