Hey sorry about your little one having a ''poppy knee'' (thats what we here call them and we have seen a few )
We have had them operated on and to be honest i think it was the best (for us and our little girl) all round.
We took her in,in the morning and our vet whom we trust 1000000% worked his magic,yes she did have mobility problems after the op,and yes she had to stay quiet,and yes it was hard work on all.....but she got to be pain free and she even started to jump again...so for us it was worth it.
I will say that she had to have it done twice simply because the grove to hold her knee in place was still not deep enough after surgery so she had a pin placed there to stop it popping,no it wasnt painful to her....and yes i would have known,she would have point blank told me if anything was bothering her.
Cost wise it came out at around $800.
I suppose the best thing for you is to go to your vet and discuss whats the best option for you and yours.
hope it all goes well