She should pay for the roads she uses, but taxes don't pay for usage. There's often overlap between taxation and usage, but there's no guarantee. For example: 
  
1.) you could pay a tax for X and not use X (like public schools for the childless or those who take their kids to elsewhere) 
  
2.) you could pay no tax for X but still use X 
  
3.) anywhere in between. 
  
If she wants to pay for usage, she should want a system like the supermarket: you get billed only for the products you actually use. 
  
(I suspect though a more fruitful discussion would as to why she isn't curious about your ideas and puts you down...)