My suggestion: DON'T be there. YOU have the sentiment of, "Oh, I feel I should be there for her for her last moments..." The thing is, they don't know the difference. They don't know what's coming. One moment they're in pain and depressed, the next moment they're free of pain and gone.

I've done it both ways -- I held my first mare, the grey arab in my avatar, because I felt like it was my duty, and because there really wasn't anybody else there to hold her (besides a stranger). A couple months ago when my 3 year old buckskin gelding was euthanized, it was at the hospital and there were extra hands there, and I just couldn't be there for it. That was MUCH easier (then again, I only had him for less than a year, as opposed to 7 years with my arab).

Working at an equine vet hospital for almots two and a half years, I know personally that vets prefer the owners not to be there. Also, it seems like if ANYTHING will go wrong with it, it'll happen with the owner there. :-\

Also, if you have never seen or helped a horse be eutanized before, DON'T HOLD HER HEAD. They go down /hard/, especially with sedation -- it's rather surprising if you haven't experienced it before. One thousand pounds of meat and and flesh make a very hard, loud THUMP when they hit the ground... And you always want to try to make it an easier fall, but most of the time you just can't because of all that force pulling against you. And really, they're already dead when they hit the ground so it doesn't matter.