I lost a friend today

My dog Kara was 11 years old. She was my first dog I got on my own. She had such an amazing personality to her. Just an amazing dog. We had to put her down today because she developed cancer. I feel awful because we saw signs she wasn’t doing well but instead of taking her to the vet I kept saying we should wait and maybe she would improve. Unfortunately she didn’t and I have a lot of guilt.