Hmm, not uncommon for old wrist injuries to become painful years on. Especially if it was an old Colles facture that resulted in a shortening of the radius and therefore upsetting of the whole carpus. She could have slept on it in an end of range position and irritated something there. On that does she have any metal work in the wrist?
Go back to basics as a first step. If she has pain at passive end of range (EOR) and also on resisted movements, I assume isometric not through range isokinetic/isotonic mvts? and also point tenderness then it sounds more joint related.
How are her upper limb tension tests for the brachial plexus? This might be a factor and would be worth testing. If you wish to treat her conservatively in the first instance why not provide her with a wrist support to wear for a week or so and treat the joint issues as you chose. Mulligans MWM's might assist if it is a join tracking issue.
Any more info would be great 8o