Other mistake: During the trial near the end, Fletcher is grilling the lover about having sex with the client every time he went over to her house. Watch his face. He starts to say something, but the scene cuts and the other lawyer says, "He's badgering the witness." It's likely the next line was the man admitting to it; however, an extra scene or two was inserted before he ends up saying it.
Continuity mistake: Audrey's cup disappears when Jerry sees Fletcher through the plane window.
Continuity mistake: Near the end, when Fletcher is giving the homeless man some change, notice how the man has a bright patch of light on him. In the next angle it's not there. Cut back to the wide shot and it's back.
Answer: First of all, she's not "on the hook" anyway...this is a divorce proceeding, not a criminal trial. And second, this film has multiple inaccuracies in its depiction of the legalities involved (see Legal Eagle's two-part analysis on YouTube for a very good rundown); the fact that no-one brings up fraud is the least of them. It's not important to the plot, so it is simply brushed aside, counting on us (the audience) not worrying too much about it, like so many other lapses of reality in comedy movies.