Sorry I didnt see the part about the trainer and being abused. Thats horrible! I would suggest positive reinforcement to get her comfortable with training again. I wouldnt even use a leash, in your house or backyard. And let her become more comfortable with that type of "stress". I cant even imagine what that "trainer" put her through but it must have been frightening.
Mace vom Misteri, FO ~ GSD
Ryot ~GSD (my true heart dog RIP)
Apollo vom Deutschen Adler ~GSD (rehomed)