I’m so sorry you lost Bun.
The meds your vet prescribed plus sub q fluids and the examination incl x-rays to make sure there wasn’t a blockage is the correct way to treat stasis. I’m sorry it wasnt successful. It’s sadly not very uncommon, but it’s still so, so sad.
As you know, stasis is a symptom rather than an actual illness. It can be a symptom of a wide range of problems, from something very minor to something really grave. Rabbits hide illness extremely well and once they become symptomatic, they are often very poorly and go downhill quickly.
I dont think anyone can give you any good answers as to why this happened. An autopsy may provide some explanation, but often those too are inconclusive. Not knowing is very hard though.
It’s very difficult to cope with the loss of a rabbit, but it’d be unfair of you to blame yourself. As you said, Bun had had bouts of stasis before, and you had the appropriate meds at home. The vet wouldnt have done anything different at that stage, because there wasn’t a blockage.
Grief needs time, often a lot of time. Bun was deeply loved, and she loved you, and that’s what matters the most.
When you feel up to it you are very welcome to post a few pictures of her here and maybe tell us some fond memories of your time together. Some people are helped by painting or drawing or embroidering a tribute to their lost bun.
We are so many here who have experienced loss of a beloved rabbit. You are among friends here.
Binky free, sweet Bun 💗❤💖