Will try and answer a few questions.
She does know how to use the fog lights as she called me the first morning it was foggy so I could show her how to turn them on. They are on a switch on the dash board so she won't be using them accidentally.
As I've said I thought it was maybe bumps in the road but it happened when I was in her car and it was definitely flashing.
We've had the young boy from round the street come round at tea time to check the lights and he says there is no problem with how they are set or how she says she is using them 
She's a sensible girl and pretty clued up and it's driving her mad as much as me.
My car is higher then hers so I'm going to drive past her again tonight in dhs car when it's dark which is lower to see if that shows anything (like I say it's driving me mad)
I was hoping someone would say "oh I had then once and it turned out to be xyz" but everyone seems to think like me that it must be the lights.
The car was Mot'd the day before we bought it and we put it through a service a few months after and no problems were picked up. Dh (not a mechanic) and neighbour (is a mechanic) have both looked and can't see a problem and I've driven past her in the dark and can't see a problem.
Most people in NI are good about the whole new drivers/45mph thing. It's obviously not ideal if you're on a long winding road and can't pass but it's a bit like being behind a tractor- bit of a pain but you have to accept it.
This always happens with oncoming traffic though who won't see the R plates I only really added it to my post to show that she's not speeding and other drivers are thinking she's a hazard.
The app I was talking about was through her insurance company Adrian Flux. I have it on my phone and she has it on hers. Every day I get a list of every journey she's made in list form and if you click on one of the journeys it shows you a map route and the whole route is marked green/Amber/red so you can see how well she's driven at every part of her journey. It's great for new drivers and scores there driving and shows how much they can save at renewal if they carry on driving well.
At this point I'm getting close to asking all Belfast Mumsnetters to drive one way along Newtownards road while dd drives the other way and you can all report back to me.