Well, there is no perfect/infallible setup for a farm wide dog, and all you can do is do your best, especially with cattle fences.
Sorry this happened tho and I've lost a couple over the decades to the same thing..
That is just absolutely Terrible!!!...........I know from experience that ya can play the "what if" game for days and weeks on end.....but, it never makes ya feel any better....it never changes the result.....and, everything isn't in your control to change things that are meant to be. There are some things that just happen that is difficult for us to make sense of, but ya just have to have Faith that the Father in Heaven has a reason for them to happen.....I know it is devastating for the children too, so please give them a from me too!! It will certainly be a bit, but things will get better for ya....just don't lose Faith!!
That is just so hard to hear! My deepest condolences on yet another tragic loss. I hope it was quick and painless for her. Please don't beat yourself up too badly about this.
Please don't feel guilty over this. Pain, sorrow, even anger, yes but no guilt. You took that dog in, gave her what she needed and wanted. She was loved and knew it. She was happy on your homestead and that isn't something that everyone can say they were able to do for a dog brought in from somewhere else.
I'm very sorry for your lost as myself and family have gone through this as well. There are too many things in life to be guilty for, don't let this be one of them.
Not enough words for comfort.
Try not to feel guilty. I agree with @mystang89 that you gave her a good life and she enjoyed her freedom. Accidents happen, so don't beat yourself up. Tie you up a punching bag down in the basement or out in a tool/machine shed and take some good whacks and maybe kicks at it. Good cardio and could help with what you're holding in causing that ulcer.