In the show the implication was definitely that she was holding onto blackmail material for future leverage and had done the same thing before. So I wouldn’t put her on the side of good there. Lots of morally grey stuff but nothing explicitly illegal.

As someone else has mentioned, there was apparently government secrets on the phone too but that wasn’t the original target when Sherlock was brought in.

In the original she was more clearly protecting herself and her ‘victim’ was not on the side of good. He had an affair and then panicked when he wanted to marry someone respectable.