Reasonable concern (the car thing). I'd consider getting her involved in the route planning - the Wisc. Dept of Transportation (or Dept of Tourism?) likely has a map/guide to preferred cycling routes - you could look for it online yourself, but get her invested in your trip by "helping" you look. And/or, contact bike clubs of whatever mid-large size cities you'll pass nearby & ask for route hints. If Mom feels she has some control (i.e., safe route planning), things will go smoother.

Acknowledge her concern about Bad Guys - although, of course, most thugs live in cities, not remote campsites - and agree to sleep in State Parks or Private Campgrounds, rather than rustic forest areas or "stealth camping". I HATE staying at state parks in a tent - but you're negotiating here ("You give me your blessing & happily see me off, I'll follow your recommendations about safety issues.") For next year's trip you can stay wherever you want.