I found this article that could shed some light on the 'silver' angle:
http://medievalscotland.org/problem/names/arianrhod.shtml
If you want to Google further yourself, you can use 'Arganhell' (given as the oldest known form of the name) and 'Ariannell' (variant with two n's instead of one) in addition to simply 'Arianell'.
Rene
www.AboutNames.ch