Hi Jenny
Didn't realise this was actually your bitch with the umbilical hernia - as you can see from the replies on Champdogs, there are lot's of different opinions out there
Only you can make the decision whether to breed or not from your bitch. I'm afraid I don't view vets as the font of all knowledge when it comes to breeding dogs, particularly young, newly qualified ones. Many of them are quick to leap on relatively insignificant problems but are curiously unaware of the serious problems in a breed eg FN & PRA in Cockers. I don't know whether you have heard of the geneticist, George Pagett? His approach to breeding dogs is that you should prioritise hereditary defects - definitely don't breed from anything affected by or a carrier of a serious problem but with less significant things, then it's a case of not throwing out the baby with the bathwater
Good luck with your decision