There are no rewards for Franklin and Michael, though she is a possible Altruist Victim if rescued with Trevor
Head to the marked location and watch what is going on. Some of the Lost MC are kidnapping a woman. The best thing you can do is wait until she is thrown into the back of the van. If you start too soon then the woman can get away and you fail the event.
Once the woman is in the back of the van, start shooting at the tires of the Lost MC Van. Take out 2 or 3 tires and they will get out and attack you. Kill all of The Lost who come after you.
As you travel along the Great Ocean Highway you will be attacked by more Lost. Simply knock them off their bikes with your car or gun them down. Run over anyone who survives. Just get her home to be thanked.