Hi,
I have a niece one year old.The doctor over here says she is suffering from hypoxia and cerebral edema.
Suggest me the treatment .

What has YOUR medical professional suggested?

These are serious conditions that should be treated immediately. You/her parents should discuss this with her doctor (or get a second opinion from a different doctor) rather than asking for the course of treatment on the internet.

The doctor suggested medicine "Valproate" and "physiotherapy."

Hypoxia means that the child is not getting enough oxygen. This can be life threatening.

Cerebral edema means that there is swelling on the brain.

The internet is the last place you need to be getting advice from. Get a second opinion from a live pediatrician if you are not comfortable with the advice given from your current doctor.

And also her report says

"MR imaging of brain reveals abnormal periventricular white matter
hyperintensities and associated volume loss in bilateral
temporo-parieto-occipital regions,with thinning and
hyperintensity/gliosis of posterior body and splenium of
corpus callosum,as described.
Imaging findings could suggest sequelae of perinatal
hypoxic ischemic insult/periventricular leukomalacia
Clinical correlation is suggested."

Where is 'over here'?
Does she have epilepsy?

Has she been diagnosed with cerebral palsy?

Over here means "New Delhi,India" and the answer is no for cerebral palsy