I have inherited the gift to see different sides, all in their own right and with their own values and deficiences. Because of that, I can help members having to make difficult decisions where there is no clear right or wrong to work out where they stand, but sometimes the same can also help those with a huge emotional hurt to show them the other side of the picture in order to give their thoughts a new direction and help them on with their grieving process.
What has happened to Buffy is a tragedy, no doubt about that! She had one of those very random bad reactions to even a small dose of GA. With her, it would have likely otherwise happened the first time she needed an operation or any procedure under GA so I doubt that she would have grown very old.

Buffy was one of those sparkly stars that burn very bright but only shortly. Try to remember her for her big personality and the joy she has brought to your life and treasure for having had her in your life.
However, the decision to have the cyst removed was a valid proposal in view of the alternative. I would have made the same decision to have it removed for any piggy of mine as well and would have made the same decision again for another piggy of mine, as hard as it always is when the same issue comes up again after any failed procedure. Talk about very deep breaths and major jitters! I hope that this helps you? I have been through it more than once with other health issues with piggies of mine needing certain operations.
Please be kind with yourself, make sure that you work out the adrenaline excess which you are channelling into your anger in a physical way as well as processing the big shock mentally. It will take its own time because you have to deal with both the trauma of the shock and the trauma of the loss at the same time but you can process only so much at any given time. Brace for the adrenaline 'hangover blues' once your anger/adrenaline high is finally running out.
We are here for you to help you through it at any stage and for any questions or understanding support if you need a soundboard. Just please use this one thread which we can run for as long as possible. It may help others reading it when they grapple with their own overwhelming loss down the line to know that they are not the only ones - and that is not the worst legacy Buffy can leave. The grieving process is nothing like just feeling sad; it is so much more complex.
PS: Being able to help others does help to boost my own mental wellbeing and makes me feel better in myself; which is important for my own recovery from a serious illness and a rather close shave. I can't just sit around at home for months and feel lonely and terminally bored.
But I only do it whenever I do not feel stressed when reading the first post; I have to put my own needs first but I am still the same person as I was before. The community on here is my lifeline and is helping me as much as I am helping them.

And while I am more aware of my mortality, I am also more aware of the need to make every day I live - how many or few that is going to be - count by leaving the world that little bit better. This way, it doesn't matter how long or short I live because I have lived it to the best I can.
Try and see Buffy's short life in terms of quality instead of quantity as well - both for her and for you. I have had some piggies of mine only for a short or very short time (a couple of times only for a scant few weeks) but they are no less precious to me than those who have been with me for a very long life because they have added some special, unique sparkle to my own life without which it would have been a lot poorer. And those sparkles will always remain with me; I can access them whenever I need to remind myself of the good things I have had and still have in my life instead of fixating on what I won't have and can't change.
PS: I am very lucky and blessed to have access to the best possible treatment (thanks to whoever went back to my biopsy and found the crucial mutation) and to have got that access just in time. The brain doesn't have any pain sensors so symptoms were very vague and I never had a visible recognisable melanoma spot in the first place... Life is life; it is not about fairness or entitlement.
You have given Buffy the love and happiness to sparkle and to add that sparkle to your own life; please don't throw it away. It doesn't matter so much how long she has sparkled for you, it matters much more that you have her sparkle added to your own life.
What happened was not foreseeable or in your control but all the daily care and love are what really counts because that is very much in your control and you have not failed her one bit in that respect. What you have done, you have done out of love and wanting the best. What you have no control over is the outcome. There is never any guarantee.
Just give yourself time to work through your anger and slowly think things through more as your mind frees up more. It is not an instant process but I have been hopefully able to snap you out of it enough to start processing.
HUGS