My daughter has congenital hydrocephalus ,she was born at 35 weeks.How severely can it effect her development?

My 20.5 month old daughter was born at 35 weeks ,1 month early . She was diagnosed with congenital hydrocephalus at 8 months old. She's 6 mos.delayed developmentally. Shes at a 8-12 month level with her fine motors skills and 9-15 month level with her gross motor skills.They are saying shes globally delayed. Her doctor said the hydrocephalus should go away on its own ,a year ago, Now hes concerned it may be affecting her development and is ordering a cat scan of her head. My question is, How severely can hydrocephalus delay development?