It depends on the hill, but if her bike has a hub motor, the Townie should suffice (and being a "Trek" you'll receive good CS). I prefer mid-drive systems for really steep terrain because the power is magnified by the drivetrain, but hub systems are fine as long as you can maintain half of the top speed while ascending. Otherwise too much energy is transferred to heat which can be deleterious to the motor. Best case, test ride whatever you're considering.