I have a Giant LaFree E+1 with the carbon belt drive and IGH. LOVE it! Tackles hills like they aren't there, and the motor is exceptionally smooth with great torque and 5 levels of assist. Battery is rated at 63 miles depending upon assist level used. I'm finding real world mileage to be 54 because I tend to have fun using the Sport+ mode (highest assist) a lot of the time. The Small is the perfect size for me, but... I am 4" taller than your girlfriend, and my bike retails at $2,700 which is over your price range.
Maybe you should look at a folding ebike for a smaller size? Or a kit to install on a bike she currently owns? Or tell us what you've researched and let those owners who have those bikes chime in.
Last edited by momsonherbike; 10-03-19 at 12:54 AM.