Hi Ashik,
Window light can be excellent. A good idea sometimes is to use a white card on the other side so as to wrap more light to the shadow side. Then you can shoot in manual with the same aperture but with a faster shutter speed if you wish. In any case, you can decrease the bright areas on here face which have so much light that detail is lost. Those areas may still have information hidden there.
What camera are you using. Also what software are you using. If your camera can give you a raw file then these issues can be often solved in the software. Still, opening up the shadows a little by having either reflected light or a fill flash is something to think about.
You certainly have a willing model!
Asher
P.S. I hope you'll answer the question on what camera, software and espertise you have, so we know the type of feedback that you might find helpful.