When you adopt a pet you commit to giving them the best life possible. That doesnt necessarily mean with you. People move, have children, add new pets into the mix, etc. Situations change and sometimes the pets we love so very much simply cannot adapt for whatever reason. You said you have already tried very hard to train Roxy, but it isnt working. At this point keeping her would be putting her in a no-win situation. There is absolutely nothing wrong with rehoming a dog under these circumstances. The important thing is that you love her enough to see this and are willing to break your own heart to give her a chance at a better life. Thats admirable, not something to feel badly about. I really feel for you and wish you the best of luck in finding her a great new home.