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There has to be a specific cause for her to lose the function of her hand. It could be related to the musculoskeletal system or the nerve or blood supply to the tissues in the area.
In some cases of
severe joint pain such as in
osteoarthritis, there may be restriction of movement to minimise pain.
If there are any conditions such as trauma,
diabetes,
vitamin deficiency, compression , these could affect nerve function. These are only a few of the conditions that could affect the function of the nerve supply.Normally if the nervous system is involved , there may be complaints such as numbness, tingling or other altered sensation.
She needs a through evaluation of her right upper limb and neck, you may want to consult a orthopedic specialist.
She may at some point, be referred for
physiotherapy in an attempt to regain function.
I hope this helps