Hi Laurent,
I cannot be of much help because I am not a doctor and I am not familiar with the problem you described. But I found this doctor's response to someone who posted on the Doctor-to-Patient Asthma and Allergy Forum on 5/23/07. You can find it at
http://www.medhelp.org/forums/Asthma-Allergy/messages/53.html. The person asked about headaches and nosebleeds. The doctor responded:
"It is most likely that the nose bleeds and headaches are unrelated. But both headaches and nose bleeds could be caused by a problem with your blood not clotting properly. In this case, you might bruise easily, bleed a lot from a small cut and have bleeding from your stomach or intestine. If the nose is the only place you have bleeding, a clotting disorder is unlikely. There a simple blood tests your doctor can order to see if poor blood clotting is the problem.
There is an association between Migraine Headaches and nose bleeds, seen most commonly in children. This could however also occur in adults and, since Migraine Headache is a very common condition, you might want to ask your doctor to check this out first.
If neither of the above is the answer, there is another possibility. A different type of inherited disorder that can involve blood vessels of the lungs (most commonly), skin and even the brain. These are called arterio-venous malformations (AVM's) and are uncommon but not rare. One of these is called HHT. You would have to ask your doctor about this and it might be necessary for you to see a Neurologist. You will probably need to have a CT Scan of your brain to evaluate your brain for this problem and other problems that could cause headaches."
It sounds like a clotting disorder might have been ruled out in your girlfriend's case, if they included it in the blood analysis.
The scan of the brain might have ruled out the AVM, perhaps depending on the type of scan your girlfriend had. By the way, I take it that your girlfriend has not experienced any head trauma recently?
It sounds to me like there are known associations between headaches and nose bleeds, so perhaps you and your girlfriend need to see a different neurologist!
I don't know what to think about the doctor pressing on the back of your girlfriend's head and making her nose bleed instantly.
I wish I could be of more help.
Good luck,
S~