Pretty sure she is on a petrol one - there is a fuel tank above the front wheel, and you can see the fuel line going into the throttle body above the single piston engine. You can also see the exhaust and muffler below and behind the piston.

Also looking into it more, I don't think the Autoped was ever offered with an electric motor. Apparently the confusion comes from the fact that the company was bought out by the battery manufacturer Eveready, and sold as Eveready Autoped. Eveready modified the Autoped by adding a battery and ignition coil, replacing the original magneto system, but propulsion was always by means of a petrol engine.

I don't think the one in the photo has the battery and coil however - the coil can be seen here in front of the gas tank, but is missing in the OP photo.

Edit: looks like the batteries and coil might have been separate - here is an article from 1917 that describes the Autoped as having a magneto ignition system (no coil) and also a battery box to operate the front and rear lights. And here is an example with an ignition coil powered from the wheel, but no battery box and no lights (which were probably optional) The one in the OP does appear to have the battery box and lights, but uses the magneto ignition, so it's the same model as described in the article.