Agree with [MENTION=2071]Davidh[/MENTION]
Well that is a hard decision there, one that will need some thought. If you have the money and the want for another pup, then this may be the answer. I think the breeder is trying to help out and that is great, but it's up to you if you want two bullies. Molly will need a lot of your attention when she gets worse and playing with the pup could cause her more pain. It is hard to keep them quiet when there is a play mate close by. I also would not take the pup and then if it does not work out, just give it away, especially to someone who could not afford to buy one, because if they can not afford to buy one, they can not afford to take proper care of it with the vet bills and such. This is just my two cents worth. I'm sure you will make the right decision that is right for you.
For all you know right now, Molly might not get any worse. From what I gather, surgery is only recommended when the arthritis sets in. If you keep her trim and exercise her arthritis might never set in. If it does, it does but I try to cross bridges when I get to them.
I would grab that puppy before she changes her mind and the very next day sign up for the insurance with the options pack.
Which insurance and what options pack? seeing that we are picking up a special bully, I dont know what they would or wouldnt cover - PM me if you want