Terrible news and a terrible thing to go through, you have my sympathy and condolences! Earlier this year I had to put down my cat who was 19 years old and I have had her since I was 10. That was extremely difficult, but the cliche of "time heals all wounds" holds true here. Just keep your head up and try to focus on the good things and do not dwell on it. You will soon be able to look back on her with fond memories!