hey welcome here..
first of all hope your mother has been excamined thoroughly by a doctor. ???
it is not always as easy as one could wish, If the pain is from neuropathy from the diabetes , many get a medication called Gabapentin that help a little and some have a little help from taking 600 mg daily of R-alpha-lipoic-acid
the best to do is then also to go so low in carbs that ones blood glucose is in the non-diabetic range if possible, that means to very many very low carb, like under 50 grams a day... but worth a try, it does mean to change ones eating style radically..
like not to eat sugar at all and avoid bread, rice, potatoes, cake ,fruit, and all drinks containing sugar..
some really have a good effect of going really low in carbs, but many oly get a little bettering and probably avoid further progression of the bad condition ...