So they ruled out a soft palette?

Did you try tying her tongue AND putting on a drop noseband? Try also giving her Airway gel and using a nebuliser on her. Try also giving her a Rakelin injection once per week to calm her down. Our filly roars and the vet said we'll need to retrain her to swallow when she's racing. She tends to stop swallowing when she gets stressed by work and then roars, cuts her wind off and gets more stressed - it becomes a vicious cycle. If the above doesn't work, you may need to get her operated on.

You can also try Glycerin or Wind Aid over the tongue before she works
Edit: I see you tried Wind Aid