Using a rationale of, I think the extra weight is causing her joint pain. Only fruit for dessert, regardless of what others at table are having, bread only if in the form of a sandwich, and only 1/2 a sandwich, 1 piece of toast at breakfast, no sugar in tea, coffee, only fruit for snacks etc. Also mother refuses care, becomes physically responsive to staff, family insisting that she is made to have a bath/ shower.
It would help to know first how valid the assumption is that extra weight is causing joint pain, absent any other identified medical conditions. If this is just the family's observation, I'd take it with a grain of salt unless it's corroborated by medical opinion.
Also, has the facility doctor made an observation of this, or has an orthopedic doctor been consulted? if the staff concurs with the diet, is the patient resistant?
I get the impression from your last statement that there's more going on here than just the diet and weight issue.
I do think though that if the family is making an issue out of either what she eats or her weight, that it would be appropriate for staff to counsel them that their attitude should be supportive, and that the medical staff could more legitimately handle the weight issue.
It's hard enough to be in a facility, away from home, probably not feeling great in the first place, w/o being nagged about what she's eating, especially from the family.
This lady's diet sound too restrictive so a consultation with a dietician is in order. She may need to loose weight but it should be done with a sensible amount of food. things that need to be cut out should be reduced gradually, then she may not notice the lack of sugar in her coffee.
I'm not sure what you mean by refusing care, becoming physically responsive, etc.
Does the patient have dementia?
Do you mean the patient attacks staff because she doesn't want to bathe?
I think I'd be thinking about my legal situation as well, so start documenting. Is the proxy someone with medical background? What other characteristics have you observed about this person?