I am so sorry for your having to go through this
I just lost my boy about a month ago - he was only three
went in the middle of the night and god I wished I was there
comforting telling him he'd be alright and happy and at peace
I know it'll be hard to watch but I think it'll help your mare having you there.
If you chose not to I'd understand that too, it's all you.
No one can tell you what to do.