The fact that she is/was the Governor is not enough to show inappropriate conduct.
If they want to complain that as gov, she should not have accepted the donations, her defense is that her status as governor made her the target in the first place. The fact that she is/was the Governor is what triggered the initial unfounded ethics complaints. They can't say, we get to take all these free shots at you because you are governor, but that status also forbids you from accepting any help to defend yourself.
If any public official is expected to personally finance every ethics probe legal defense, you have just provided the opposition, liberal or conservative, a way to hound any public official out of office.
The law is expected to be blind.... but not stupid.
“To make anything stick, they would have to show that a benefit inured to the donor as a result of the donation.”
Indeed. And they are not going to find anyone who benefited for a contribution of $150.