I've been told that oral meds aren't as effective on snakes as it takes too long to digest and metabolize the meds and they loose their effectiveness in the process. And you certainly don't want to inject it into the prey that would take it even longer. Not sure what you are dealing with but your vet should have given you injectable meds seeing that he hasn't have someone hold her lower portion and keep a firm grip and just get it done - once she figures she can't get away she'll mellow.

Good luck.