Durham's Rock Hard Water Putty, avaialable at your local home supply or hardware store, is great, read the label it's got tons o' uses.
Maybe not flexible enough, but using Patrick's lost wax process it could be poured into the mold, removed when hardened and painted or gold leaf applique' to replicate piece. Perhaps a measurement of the Syren's preferred appendage would allow it be cast in a size that would fit her.
Just a thought, the stuff is great.
Jim