
there's no way you could have known. the job of a vet is to identify and explore these issues, and you are no veterinarian. neither of you could have expected that a small murmur could've been this serious, especially if it only showed up on this yearly checkup. you did everything you could have done, so many pet owners don't even do yearly checkups. i'm so, so sorry for your loss, but i'm sure she loved every second she had with you and you gave her a wonderful life!
please do not beat urself up, so many ppl with big hearts including me would honestly prob handle ur situation very similarly. life is crazy and unexpected sometimes and the last thing u need to do on top of that is beat yourself up. if anything, please be more gentle than ever on yourself, it is hard enough as is to grieve 💗 sending u so much love