There is no solution!
Reflectives are good but have a huge flaw. They work well if in the direct light beam, but once you are in the periphery or even in front of a vehicle using dipped lights (like the majority of cars in an urban environment) they do not really light up like you would hope. I have done this experiment myself (cue much prancing around in front of the car at night by Mrs Skol while wearing my sample jackets) and found that only being caught in the full beam reflected any light in an appreciable way.
Pedal or ankle reflectors will be the best as these are moving and also more likely to be caught by the dipped headlights. The most efficient means of being spotted has to be decent bike likes. This MUST NOT mean cheap, dazzling super-Lumen Chinese lights but an effective, well angled light that is bright enough to be seen without being retina burning.
Unfortunately this is still no guarantee. My bike lights fall somewhere in the middle between the wet candle LED and the Super Nova explosion bike light and I still experience many drivers simply failing to register my approach even when on an otherwise empty road.
By far the biggest risk to cyclist's is not when directly in front of a vehicle's headlights but when approaching from the side, I.E at junctions or roundabouts.
Tell her to ride defensively and expect EVERYONE to try and kill her. Sorry, but it is the truth!
EDIT: Forgot to make the point I had intended to highlight. If they are not looking the they will not see you, regardless of what you wear or which lights you use!
Highly illegal but also highly effective, purely for the abnormality of the situation that catches the attention of motorists.
