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...)