Oh my heart goes out to you and your family, my prayer's will be with you all.
This almost happen to us about 2 months ago, getting home from work we let the furkids out to use the restroom while unloading the car. I notice only Buffy was back and I told hubby where is your son, I bet eating grass again.
I looked out side and Duncan was on his side...long scary story short we pulled out a thick, hard peace of grass ( St. Agustin grass) it's like a vine.
We were very lucky he started breathing right away and is fine.
I do hope you have her body check to see what caused her death and again I'm so sorry!