One point you never realise is that your 7 speed starts with 14T at the rear gears    While the normal 8/9/10 speed starts at 11T. Presume you pedal at the same cadence on the same terrain, using the same 53T front chain ring. One revolution from the 7 speed at the highest gear is 3.78 revolution of the rear wheels and if it is the 11T for every revolution it's 4.81 turns!  For every turn of your crank, you lose 1 turn which is 406 cm and if your cadence is 60 turns per minute and that's 406cm x 60 = 24360cm. That means if you turn the crank at the same cadence with both of you on the highest gear , you on 14T and hers on 11T (presume both of you can do it lah!).you will lose 243.6 meters every minute 

She right though, it's the gearing. Cadence is another important factor, pedalling furiously also tires you out faster. I mentioned it before in the earlier threads. Gear inches is also important for hill climbs. The smaller the gear inches ( GI ) the easier it is to pedal but at the expense of speed. Easier to pedal even uphill, the slower the wheel turns. For a 7 speed  with 14T to 30T which is yours, the range is from 75.71 GI to 35.33 GI. And for a bike with 10 speed with 11T and 36T, the range is 96.36 GI to 29.44 GI. That means, the 10 speeder is advantageous from the highest gear and also in the lowest gear. This is just the rear and we haven't talk about the front chain rings yet! 

And let's compare with an MTB to actually explain the difference between an MTB and foldie. Presume an MTB at the lowest gear which is 30T (front) and 36T rear, that's only 21.6 GI and that's almost freewheeling, very light to pedal. The other end which is 44T (front) and 11T (rear) the gear inches is 104 GI. Now let's use the same GI, meaning the same effort needed to pedal at the same cadence. We use the highest gear on your foldie (7 speed) which is 75.71 GI. For every minute you travel , 53T front and 14T rear X 60 rpm cadence. That's 922.2 meters per minute. Let's take MTB (26 inches) using the same effort at approx. 75.71 GI. That's 44T front and 15T rear which is about 76.26 GI, quite near! With the same effort and the same cadence, the distance covered is 1091 meters. That is approx. 100 meters slower every minute.