The element in the front glass sunroof.....

is that an aerial or a a demister.

The reason I ask is that she also has an aerial on the rear tailgate and I'm not sure why there might be 2.

I'm not sure of the actual answer in this case, but a lot of Japanese vehicles had two aerials as the FM radio used what is called 'diversity' reception where the receiver automatically selected the strongest aerial signal on the fly. By using two aerials spaced a little distance apart the signal is far less likely to fade in both at once due to the wavelength. My station wagon has an aerial in each rear side window, for example. In your case it could be a demister. Demisters have two wires i.e. power and ground, one on each end of the conductive trace, where aerials (usually) have only one wire which is usually connected to an amplifier box right beside it.