So sorry to hear about Rosie.
One of my spaniels, Buffy, was diagnosed with luxating patellas the day after we brought her home.
I too was absolutely devastated - the vet said to give her back to her breeder, but we already loved her - having chosen her at 2 weeks and visited every week until we collected her at 8 weeks.
She is not as robust as our other dogs (we have 5 altogether) and I feel desperately sorry for her because she has to rest much more than the others (or than she wants!!) but I know its in her best interests.
We have chosen not to have surgery yet, and all the while she is fine in herself and not in pain, we feel she is better having quality of life with us and the rest of our gang.
Hope you will soon start to feel better - it gets easier with time, but I still find myself telling people often that she is "handicapped" as otherwise they wonder why she can be a bit awkward and bad tempered! She is my baby and I love her and all the time she is not in pain and the happy, smiley little girl she always is, then I am happy too!