Barli Bear

In case you don't know Barli's story, here you go: In February, my sister-in-law who volunteers at the humane society in Bryan texted Tom and told him about a brindle Boxer puppy at the shelter. She told us that the puppy had a broken leg. Tom told me about her and I was convinced that we had to save her. Tom was the first approved applicant, so the puppy was ours. 
We named her Barli (little bear) and she stole our hearts. Tom took her to a vet down here to have her leg looked at and the vet gave us two options: amputate or try to save the leg. We chose to try to save the leg, even though it was more expensive and not guaranteed to work. Barli had surgery to put pins in her leg. These pins were in there for about a month and a half. She couldn't be a normal puppy during this time. She couldn't run or jump. She cried a lot and was on constant medications. When her pins came out it was such a good day. We had a "normal" puppy. 
Fast forward to May. We had noticed that Barli isn't walking right. This has caused her to put pressure on her paw and the pads on the bottom of her paw were wearing away. We took her to the vet in Mansfield and he gave us some medicine to put on the pads. By June the problem hadn't gotten any better. We had an x-ray of her leg done and it seemed like the bone didn't heal correctly. This is what was (possibly) causing her to walk wrong. Dr. K told us we might have to amputate a toe. 
Fast forward to yesterday. The pads were STILL gone (think bloody paw prints everywhere) and an abscess had formed on the side of her foot, too. I took her to the vet in College Station today and he did an x-ray. He said that he thinks everything healed correctly, but that there has been nerve damage in her paw and that's why she walks wrong, twisting her foot with every step. He suggested we amputate the whole leg. He said that there's not going to be a way to save the foot. Of course, we are going to get a second opinion from Dr. K, but how do you look at your puppy that you've come to love so much and try to picture her with one less leg? 
How do you decide whether or not your dog gets to keep all her legs? How do you know if you're making the right decision? How do you make that decision knowing that you can't go back? I feel like this is so insignificant when compared to other people's problems, but she's my fur baby. She's the closest thing I have to a child and I want to protect her. I want to take the pain from her. I want to make it all go away. I want to have a "normal" 7 month old Boxer, who doesn't lay on the couch all day, not eating, not playing, because she's hurting. 
Please pray for us that we will have wisdom making this decision. My heart is hurting.