I'd buy that if they accidentally on purpose leaked it ALONG WITH her son's medical records. But not instead of. That's just cruel and when it comes to children Terfs are generally not cruel.
Unless of course they were told to send her something else because there's evidence in the records of her son's medical care that they don't want getting out, and so a put upon member of staff chose the best option in their constrained circumstances. It's a very risky move though - it's a data breach so management could easily get rid of whoever did it claiming gross negligence, which it is.
Whatever the reason, i simply don't think it was an accident. It's an entirely different sort of record than being asked for. Switching up similar patient notes might be an accident, not sending something entirely different altogether and highly controversial.