I am so sorry to hear about your little Oreo! It sounds like she had a great home and I am sure she understands that you tried your best and really loved her. I had a rat with a tumopr that size but it was near her neck. It too started out really slow and did not seem to bother her. It did not get that big until she was about 5 1/2 or 6! Yup thats right she lived to be 7!!!!! I moved across country when she was 6 1/2 and gave her to a friend, she died a few months later!