These losses are so hard for we humans to endure, I am very sorry for this heartbreaking ending.
My question comes from two things you said "placenta was thick didn't look normal and liver issues with foal" --- has the mare been on fescue grass or hay? Both of these issues can happen with fescue endophyte ingestation, as well as early foal loss occuring 1 to 2 months ahead of full term. Just throwing this out there as a thought. As previously said, we often never know after these things happen.