But... she only nets maybe 30 MPG average.
Sounds like you're a little fuzzy on actual numbers. What's are the car's EPA ratings?
Step 1 is to start a fuel log (and keep it updated, religiously).
Step 2 is to get a fuel consumption gauge.
(You can't manage what you don't measure!)
Step 3 is to adjust the nut behind the wheel: 100+ Hypermiling Tips
Step 4 is to start modding: 65+ Efficiency Mods