Can i create a new ring from my grandmother's diamond ring?

Of course you can, practically. Your decision may have sentimental issues, too.

Your best first step is to pay for a certificate from a certified gemologist, who will describe the diamond in detail and as well, describe the metal, the craft of the setting and so forth. This way, you'll always have a record of your grandmother's ring.

Then, take your ring to a jeweler you trust and work with a designer to design the ring you want. You can ask that the original metal be melted and included in your new ring, which will save you money if the metal is gold or platinum.

Finally, pay for a certificate from the same certified gemologist for your new ring, so that you have documentation to compare at least the diamond with its source stone. As well, you have a base valuation for your new ring should you ever decide to sell it.