Let's get this right. You are trying to lunge your horse. You have her on the line, step towards her hip and she faces up. You step to her hip again and she faces up again, etc. etc. Sounds like to me she lunges very well, but who is lunging who? I've been there, done that.
Sounds to me you have given up 3 times, score 3 points for the horse, zero for you! Go lunge her with the attitude that failure is not an option. Have assertive body language. If needed, do more than 'tap' her with the whip. Swing the whip in the air near her. If she does not move away make contact with her. Don't hit her out of frustration. Make it very matter of fact. You warned her to move by swinging the whip near her. She just happened to get in the way. Establish yourself as the leader. Earn her respect.