can any one tell me what was wrong with liily

 

She had a brain tumour.

Not a tumour, it was an aneurysm which is a blood vessel which has ballooned out.  If it bursts it causes severe bleeding (haemorrhage). 

I am wondering why Lily never had her hair shaved when she has this brain op.

No need to shave the head. The surgeon reaches the brain through a vein in the groin, then puts small metal coils into the anurism which forms a small clot sealing the anurism.