I had to put down my brown mare, Stevie, today. Her upper leg was likely broken in an unknown way. My poor girl was in a lot of pain. It was not an easy day having her out down and locating our excavator guy to bury her. She and my gelding were intensely close. Poor guy is whinnying and looking for her. He got to smell her and knew she was under the tarp as we waited for the excavator. Fortunately a horse's grieving does not last too long but he will be looking for her for a few days. My little boys will be very sad. Losing and animal is always hard.
There is a place for animals to fill in our lives. Their own lives may be simple ones but they deserve and benefit from humane treatment. I imagine she had that and thrived for the time she was with you. She wasn't poor but only during those final hours.
I'm so very sorry. There's something somehow harder about losing a beloved horse... I think it's the having to 'hold it together' with all those extra people involved.