Sounds like the zoom meeting setting was part of the issue. Some things simply cannot be replicated online and it's unfortunate you missed that precious time and experience. With that said, old timey nurses do tend to suck the joy out of these meetings. I was never a fan of the structured discussions and preferred to see where the conversation landed. I made some wonderful friends in my mum's group and our kid's have grown up together (they're now school-aged) but admittedly the cliquey-ness of some of the mums within the group dampened the experience.
It sounds like she was accustomed to a life of privilege and only felt hard done by when that privilege was taken away. As a child growing up with 2 full-time working parents and very little money and time for extracurriculars, I would have given ANYTHING to learn the violin or simply sit on a horse just once. If she'd never owned horses in the first place, she never would have felt a loss at seeing them go. Hopefully she can get into therapy and come to her senses to realize that you did the best you could with the circumstances you were given.