For a horse that has never been wormed before, until you have a chance to really work with her accepting you messing with her mouth and shoving things in there, I would simply mix her wormer up in some sweet feed; make sure you mix it well, leave NO paste visible, make sure it is thoroughly mixed into the grain. Mix the wormer itself in with about 2 cups of feed, then add a couple more cups and mix that together, so she doesn't smell or taste the wormer so much. I've never had a horse not eat 'baited' wormer. Lol!
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."