Depends on the individual...
If the mare was predisposed to spavins because poor confo then I might, depending on whether I thought any dodgy confo that the foal might end up with could be corrected by frequent and careful farriery, and just as for normal breeding I would choose a stallion that would make up for anything the mare lacked.
If there was any chance that the spavins were hereditary, then absolutley not.
Cow hocks = spavin
Is she cow hocked? I do believe that in the vast majority of cases that this does lead to spavin. I read it in Riener Klimke's book on 'choosing a horse' and then I realised that every horse I know that has spavin is severely cow hocked without a doubt!
You could chance it by hoping that the offspring is straight hocked when born if put to a straighter stallion.
If she's not cow hocked then unless she was heavily raced or over used as a youngster ( which is a plausible excuse I think for spavin developing in any horse) then I would not consider breeding from her.
