She's right that you don't want it in TOO low a gear though. IIRC, Catrin's bike is geared quite low. I think for learning, you want it in a middle-ish gear. You're only going to be pushing the pedal about 1/3 of a revolution before you get on, so you need that to propel the bike fast enough that the gyroscopic forces of the wheel will keep you upright.

Here's a little game that might help you understand that the bike WANTS to stay upright.

Take your front wheel off. Hold it in both hands by the ends of the skewer, and have someone spin the wheel, kind of hard. Now try to tilt the wheel side to side.

That's what keeps your bike upright.