I thought it was illegal to tell the reason for termination of employment. I know in the State of Florida, an employer is only allowed to say that "yes, this person worked from such and such date" or "no, this person did not work for the company".
Seems like the former boss stayed within her "legal boundaries" but still caused her to loose the job. Only if the boss was listed as a reference (which I highly doubt), could she give her personal opinion of the OP.
Usually most applications have a question of may we contact this employer. Just check no. My aunt's resume has one job listed as "bookkeeper for car loan company - name withheld". It was a really bad job, really bad boss, but it still shows she was working in her field.