Wow yes. It must be real.... a time traveller!!!!!!
So you are a time traveller, you take you mobile phone into the past... and it connects to what!?!?! No phone networks then - no phone masts, no mobile phone companies etc etc etc.
Most likley a small radio held to her ear, or some kind of hearing aid, or anything.
Or maybe the irish film maker has actually got it wrong. Maybe she is an alien and is speaking to the leader of the planet Zob on her intastella walki-walkie.