Yup, I was with you until you proclaimed you’d never again work for a woman. Let me clue you in. The boss is just an incompetent as the trainer was and they are both at fault: Her for sabotaging good workers and he for not being aware that his star trainer doesn’t know the difference between corrosion and contamination.
I’d say silly/no cause instead of bad cause (sock color, for instance.) Bad cause tends to make me thing illegal cause. IIRC (and I may not) bad cause is also when an employee is fired without the process given in their employee manual. So if the trainer above isn’t going by the book, then there may be a basis for a complaint.
C
I had the same problem with my supervisor - she’d give me conflicting instructions and get upset when I’d do a bad job. So eventually I started typing everything out and asked her to initial it once she’d read it. She made herself look like an ass many, many times that way. I quit anyway, because there were just some horribly dynamics in that office. But I won’t go into it since I bitched about it in a thread when I quit anyway. 
Best of luck to you, and keep taking the high road and document EVERYTHING. She’ll dig her own grave eventually.