Firstly i hope your girlfriend recovery is a quick one,cotrary to belief the flashing of headlights is not a given sign that the driver flashing his lights is allowing anyone to proceed its in the highway code as a notice that the driver flashing his lights to let you know he is there and nothing else.Unfortunately everyone or nearly everyone take it as a sign that the driver flashing his lights is giving you the right of way which is incorrect,unless that has changed which i believe it hasnt YET.
Very sorry to hear of your good ladys accident. Hope shes OK-thats the main thing.Unfortunately headlight flashing has become common practice and its proper meaning has got lost along the way.A lady friend of mine was driving on an unfamiliar road looking for her left turn off. She thought she had almost reached the correct side road & put her left indicator on. As she drew alongside the turn off she realised it wasnt the one she needed but the next one. She cancelled her indicator & continued to next side road having reapplied indicator & meantime a car waiting to pull out right from the road she wanted had seen her previous left signal and WHILE LOOKING TO HIS LEFT pulled out into her path and did considerable damage to both cars. He then tried to blame her for his ASSUMPTION. The onus is on the one pulling out to make sure that its safe to do so.