Another possibility is to have her use a small plastic cable tie.
She can adjust it until it just fits over the knuckle, slip it off,
place it in an envelope and mail it to you. You can then place it on
your ring stick or mandrel to get the size no matter which standard
you are using. As a matter of fact, it is not really a good idea to
get a ring size from anyone else's sizers, ring sticks, or
mandrels--there really isn't an accurate across-the-board standard.
The cable ties I am referring to can be found at any electronics
parts house, such as Radio Shack.
Designs of Eagle Creek in Beautiful South Texas, where we are
alternating between heating and air conditioning on a day-to-day