I would wait to lunge her until after she is completely comfortable with the halter or bridle on her head and being controlled by it. Until that time, you could try free-lunging in a round pen (I suggest you get one if you can afford it). As for groundwork, I have always liked the desensitizing exercises. Expose her to unusual items, trash bag, blanket, things that make noise or could be considered scary and let her sniff them before rubbing her all over with them. If she gets scared, just stop and wait for a minute then let her sniff them again and move slower to her body. You can also start training her to yield to pressure on her side using your thumb as a precurser to leg cues for when you are in the saddle. If she has already had these things done to her in the past, it will only be a refresher course. When she gets comfortable with you, go ahead and put a saddle on her and start over from the beginning. When she is responsive the way you want and remains calm all the time, go ahead and start riding(with someone there) in a round pen.