You answered your own question.
If Mau was being accused of stealing -- whether or not she was guilty -- the prosecutor could have indicted her and dragged her through years of hiring lawyers and appearing in court.
My read on the situation is she was intimidated through threats of prosecution and told the charges would not be filed if she refrained from filing that civil rights lawsuit.
You say she was a disgruntled employee filing a "petty" lawsuit in retaliation for being terminated. If that were true, what was her former employer worried about?
If someone asks you for blackmail money or they'll tell the police they saw you commit a crime, doesn't it scream "guilty" if you pay them? Why would you pay the blackmail demand otherwise?
Same thing here. Why would you "donate" so much to a prosecutor's campaign fund if you weren't trying to buy yourself a "favor?" The feds did a lengthy investigation before indicting, so there had to be at least some evidence to support the charges.
People "donate" to those who are in high positions all the time. No different from any of our lawmakers in office (senate, house, gov, mayor, etc...). And refer to the courts ruling.
Apparently, the feds high probability to convict fell short, even after all the investigation they did. They have a 96% conviction rate and lost this one. But this is a separate issue as the feds often stack the deck, and accept plea deals to bump up their %. Guess they couldn't stack the deck as much against these people.
I say petty because she did lose in civil court. So her termination was justified, and add in this lack of evidence for Kaneshiro, et al's charges. So what she's claiming, there wasn't enough to get anything in her favor. So maybe her employer did fire her for the correct reason.
I was thinking what you thought as well, threat of prosecution if she files the complaint. But it seems like she did file the complaint and she wasn't prosecuted for the "theft". I mean, it could be cause this story broke and Kaneshiro's hands were tied.
I was in banking and caught a few employees stealing over the years. Not once did we call the police. The bank either fired them or they quit before they were fired. So "theft" is a word that doesn't necessarily mean arrest and charged. Sounds like the firm just fired her for that reason and didn't bother with the legal aspect of calling the police and pressing charges. So refer back to my "petty" statement.