I agree, this could be with something she simply did out in her paddock.
I think you started her well, and the therapist was just out of line.
Talk to your vet, and think about now, just getting her back to 100%. Start her back slow, and let her tell you how it's going.
I don't know exactly how much you were working her, but with a youngster, it's easy to over work them. They're smart and learning quickly, so our instinct is to just keep going, when really for them, it's the place to stop. I would just take it easy bringing her back, just in case, for whatever reason the work was a little too much. But really, to me, this sounds more like she slipped or something outside, rather than too much work. You seem knowledgeable and in tune with how she's working, and what she can handle.
"You're just as sane as I am."~Luna Lovegood.