I'm so sorry, she was gorgeous. I've had that happen with two of mine. I'll never understand what caused them to leave their acres and acres of safety to suddenly head into the yard where the dogs always are. Dogs will be dogs unfortunately. As much as we try to keep them separate, accidents will occasionally happen.
I think I figured out why she did it. Because of the HPAI outbreak last year, my girls are completely fenced out of the driveway for biosecurity reasons, but that creates a 'pocket' on the side of the driveway opposite from where the coop is and a handful of the girls are always getting stuck over there. Usually, they just pace over there until I come out to rescue them, and Marama has done this in the past, but I think this time she may have tried to fly home and just picked the wrong fence to hop to do so.

I know dogs will be dogs, but it's so hard to look at them right now after what they did to her... I'm sure I'll get over it eventually. It's just difficult to think of how full of life and personality Marama was, and that that's all gone now so suddenly.
I'm so sorry. It's the hardest part of keeping critters - saying goodbye to the ones we love. No matter what the cause, I always end up beating myself up for it; but in some cases, there was just no reasonable precautions that could have been taken.
Do any of your other birds go near the dog pen? Maybe a prophylactic wing clip might help.
The dog yard is our back yard, or at least ~50x80 feet of it. The hens have somewhere around 24 acres of woods that they're supposed to be free-ranging through, but they somehow always end up in the woods around the dog yard. This is the first time one of them has hopped in, though, since we put up the 6-foot fence some years ago... :/
Actually, the first thing mom and I did was trim one wing on Ihi, Marama's partner in crime. I later trimmed my Light Brown Leghorn's wing because she's an able flier as well. Thinking I may go ahead and trim the wings on my Exchequer Leghorn and Ancona tomorrow, even though they don't often fly; they're skinny and lightweight enough that they feasibly could hop the fence if they decided to. The rest of my big girls are more hefty and less able to fly (except maybe some of the Easter-eggers...) and the bantams never leave the area surrounding the coop (though, even if I trim their wings, I've seen them hop to the roof of the coop without once flapping their wings, so...). I hope that at least keeps them out of harms way in that regard...
I am so sorry pipd. My DD lost a large portion of her flock this weekend also. The great dane jumped the fence and got almost all of her birds.
So sorry to hear that... As heartbroken as I am losing one bird, I can't imagine losing most of the flock in one fell swoop...

Hugs to your DD...