I think that she tends to use fear/concern as a manipulation tactic. Hate to be blunt, but that was my impression reading the OP's original question.

Underlying this fear is the statement: "I don't want to lose you" "I need you to care about me" etc. These are real fears for her, and you must address these in many small and consistent ways. Bike commuting is (I suspect) only the latest manifestation.

Show her that you love her. Listen to her concerns. Ask her to coffee one day to talk through it - not to offer arguments, but simply to listen to what she thinks might happen, how that risk feels to her, how often it's on her mind...these kinds of things. Tell her whether you knew those things about her. Think about it some more.

Love will make a way for both of you.

PG