Catching a unhandled horse in a large herd and field

[joosie]

I completely understand that but the OP had three days to get the horse treated, really with no facilities to even confine the horse safely (a hot tape yard is NOT a safe option for an unhandled horse as many have mentioned above). Desperate times desperate measures. Would have been much worse trying to load the horse on a float in the 20 acre paddock, when she was told to leave immediately after not getting it treated.

The end doesn't justify the means. Scare a horse at this stage of its education and you have a very steep uphill climb to regain the trust you've buggered up!
Lice are not a life-or-death situation so "desperate measures" are not required.
The horse would need to be caught, or herded into a lorry, in order to leave the yard. At which point it would be contained and could therefore be given the lice treatment anyway...