Best Practices / Groundwork / Lunging and establishing Leadership with new mare?

Background: Previous horses (last 10 yrs) were well broke, older, and or well trained set up by Professional trainer, who then trained me with the horse. I have done basic ground work, never really needed much. Ride 3-4 times per week 8 - 15 miles. Not really an indoor gal less for lessons. Own a trail blazer Paso Fino Mare, and I know her well. She does exaclty what I say when I say it, and if not, I make her re do until correct. I have never had any issues with Rosa less getting to know her, she is fast, a bit hot, but knows I am her herd leader. Issue: I just purchased a 7 yr old MorAb mare, sold to me as former school horse, endurance trail horse, kids toy on loan from barn to play with, very easy going has had age 4 - 74 on her back. Laila is now a real horse (age 7), cute as a button yet sturdy well built gal. Right now, I think she would rather be in a petting zoo. I was told she did not need lunging to take any edge off (correct, I have ridden hours, and she moves on out nicely, responds well). Now that I have owned Laila for about a month, I am finding some quirks and have started basic groundwork (again) to work just as I would from the ground up. First lesson with trainer, Laila started sweet and cute, and then acted "GREEN" at best when we started basic lunging (20 - 30 minutes). She was outright nasty on the lunge, struck, swished her tail, ears back. Temper tantrum. Finally I rode her and for the first time, Laila had her head set correct (I thought I was going to have to train her head set), she stopped waltzing around snifing the ground, and was paying attention). Now, I am on my own with groundwork. Last night I found out that Laila knows many of the basics that my Paso sort of yawns when doing. I also started Laila on the lunge line and she was well improved yet would from time to time get really snotty, kick up her butt bucking, nasty look in her eye, would not focus of keep head in towards me, etc. Any suggestions? What would you do with Laila in groundwork to make her perform as she knows how to perform? She is testing me. How do I correct her nasty behavior (buck, swish tail, ears back, failure to focus and turns out head). I can't hit her with whip (she knows it doesn't hurt). Do I wack the saddle, wack a bucket, yank on line? Do I talk calmly to her, settle her down? Do I change transitions? What works best when training the "snot" out of a well trained very smart horse that does not yet respect you as the leader and is pushing your buttons and rather be petted and given treats (now she has a good work ethic, just does like it when I tell her what to do). Help is much appreciated. Never have had a well trained spoiled brat of a horse. Thank You