Here's my advice.

Pay the fine, don't turn left where you aren't supposed too and read ALL of the sign.
If in doubt, don't listen to your GF ever again where driving things are concerned. Matter of fact, get her ass to pay the ticket since she said don't worry about it. If she bucks up, just say, "Don't worry about it, it's only $198 bucks"

The law is the law. They put them there for a reason. Trust me, there is no fat guy in a large corner office saying. "Hey, let's put a sign there AND a cop stationed around the corner simply to catch a few people a day making that illegal left hand turn so they can get some Thai food"