This is a very personal decision...to be made by you and your girlfriend together. A lot depends on her feelings about the risks, your skills as a rider, and her skills and attentiveness as a passenger. The way your Spyder is equipped may enter into it, too. It is easier for a passenger to be stable if there is a backrest or footrest extensions. Your comfort level is a factor, too. You need to be honest with her if you are uneasy about taking her for a ride.
I personally don't feel the risk is too high for me, or my wife. Then again, I have raced about everything with a hull, tracks, or wheels, jumped out of perfectly good airplanes, and SCUBA dove with sharks and barracuda. Who the heck am I to judge risk? :dontknow: I have had two steering excursions, and they didn't bother me that much. A lot like wrestling an old Triumph through the dirt, or driving a sidecar rig. That is merely my reac`tion and opinion, and applies to nobody but me.
My wife has been made aware of the issues, and has thought about how to react. She has practiced the methods of recovery, although it is hard to do without an actual steering problem. She remains confident in her ability to recover, or to kill the engine, pull in the clutch, and coast to a stop, using body english if necessary to make the Spyder go where she wants, much like an ATV. She has practiced these maneuvers.
Talk to your girlfriend honestly. Search your heart and hers for an answer that will suit you both. Not everyone will make the same decision, and the only advice to listen to is that in your own heads. Nothing else counts.