Having a very similar experience with Bronco my bulldogge, I know what your going through. I like you tried all positive techniques, talked to a few different trainers, kept him on a leash inside until he was just over five months. It's good that your enrolling her in puppy school! Have you tried yelping or a loud ow, does she respond? I found with Bronco tone is important, if I'm too excited he gets more amped up, so it's a calm and quieter "good boy"! I tried turning my back to him, he would then bite at my legs. A trainer recommended leaving the room, which for me was going upstairs (basically walk up and right back down). Boy did I get a work out almost continually walking up and down lol. The first two times he sat at the gate waiting, after that when I went up he would just go eat the paint off the window sill and pay no attention when I came back down. Have you tried shaking a can of pennies or bottle filled with rocks! I tried the pennies with Bronco but when he's in that mode (for lack of better word, somebody knows what's it's called) he would just get more excited. Also tried a mini air horn, didn't work to well. I took him to petsmart and tested the various no chew sprays on my hands, he didn't like the bitter Apple. So bitter Apple became my best tool, as well as I taught kisses instead of bites and it did work. He still gets amped up in that play mode sometimes at 10 months now, a firm no works much better now as well as running him through all the commands he knows. You must be consistent whatever method you use, everytime and there is no overnight fix but you will see improvement over a week possibly or a couple weeks. I also had a trainer recommend rolling him, it worked for her if I attempt I would and have gotten bit. So that's not a method I use. Do praise when she doesn't bite but watch her body language, she may get excited like Bronco if your too loud or excited. I wouldn't personally hold Bronco's muzzle shut BC I know it would make him want to bite. I'm sure you'll get other recommendations from others, just sharing my story. Best of luck to you and your girl, she's beautiful!