Why don’t you fracture fill the crack? You can soak it in some
acetone over night, take it out, and let it dry. Then you can
fill the crack with opticon, a commonly used epoxy for filling
cracks in emeralds and other gem stones. It will fill in the
void, making it almost impossible to see, and also give the
stone a bit of stregth. I should be noted, that the customer
should be told that the treatment should be disclosed if she
ever chooses to sell it. Fracture filling is a very sensitive
subject, but at times like this, it can take a badly flawed
stone and bring it back to better than original condition. She
will be pleased. It is best to use the opticon in a vaccum
chamber for best results, but it will also work good without it.
Just follow the instructions on the label. You can buy opticon
from many jewelry and lapidary supply houses.