Oh, I am so sorry to hear about your sister in law. That must be a very frightning experience. Personally, I've never hard of this happening before...but I did a search online, and there seems to be some information on Retinal Detachment. I'm sure you've already researched this too, but just in case, here's what I found:
"Treatment for Retinal Detachment
An eye surgeon must reattach a detached retina. Laser photocoagulation, a method of sealing off leaking blood vessels and destroying new blood vessel growth with a laser beam, is another way to reattach the retina.
Some ophthalmologists inject silicone oil into the eye to keep the detached retina in place. A similar treatment is pneumatic retinopexy, in which a bubble of gas is injected into the vitreous humor, the transparent gel filling the eyeball in front of the retina. The gas bubble expands and presses against the retina to hold it against its supportive tissue. Cryotherapy (freezing) or photocoagulation will then permanently reattach the retina.
Sometimes vision lost by a retinal detachment will come back after treatment. The sooner the retina is reattached, the better the chances of regaining vision.
Occasionally the retina tears a small amount or contains holes, especially in highly nearsighted people. These tears or holes don't necessarily demand treatment right away. Your eye doctor will monitor these retinal defects at each visit. Retinal holes can be repaired with laser photocoagulation."
You are a very special brother-in-law.......... I wish I had some answers to give you, my dad had a detached retina....They did surgery on it with a specialist in this field. Dad could see but his one eye saw more shadows................ I pray that the team of drs. looking in on her can come up with the correct diagnosis. Your family is in my prayers........Do you mind if I pray for her? Diane