Is there a cure for blindness?!

Surely the poor little girl has been seen by many Dr.s since being born.

If something could be done, wouldn't it have been suggested by now ?

Optician

Obviously you'd need to talk to an Optometrist. It entirely depends on the cause and underlying reasons she has no sight. You say 'regain' but also that she was actually born this way..so it could be inoperable. She can still live a very full and normal life, if it turns out nothing can be done. But get advice & support from professionals in the field :)

It depends on what is causing the blindness. I would expect that if a cure or surgery was available, her doctors would have recommended it to your fiance.

No. A child who was born blind and is now 4 will never be able to see because the part of the brain that processes visual images has not developed due to lack of stimulation.