I would always cull any ewe that prolapsed after lambing. Once she's not full of lamb, there's no justification for prolapsing, so I'd feel that she could do it again any time - and is likely to. Having had ones who got an infection from dragging an everted uterus around behind them, before we could get the vet to them, I wouldn't wish that on my worst enemy. Sometimes culling is the kindest option.
A ewe who has had a vaginal prolapse, pre-lambing, which was controlled, and who didn't suffer any ill effects and did not prolapse again at or after lambing, I may give her another chance. If she does it again, though, culling is kinder.