My 14 year old sister suffered severe nose bleeds since she was a baby. We had tried everything but nothing seemed to work. In the end she got her nose catarized (I think thats how you spell it), it wasn't pleasant but it seems to have done the trick.
I used to get a lot of nosebleeds (at least one a day) mainly in summer, until I read somewhere that it could be due to a deficiency in vitamin K (which is supposed to help with blood clotting). Since I started taking a supplement of it (about 3 months ago) I haven't had a single nosebleed! Could be worth a try - has certainly worked for me.