Itching through B12 deficiency from Crohns

My mother has had constant itching under the skin for the past 5 years with no rash since having her Vitamin B12 injection for Crohns disease reduced to bi-monthly from monthly. Before this she had the injection monthly as the part of the bowl that absorbs this vitamin has been removed completely. No topical creams or anti histamines help and it seems to get worse in heat. It usually starts in the feet and hands, then her face and all over her body. It gets so bad that it wakes her up at night and she gets no relief from anything. Dermatologists have said her skin is fine and her diet is fine too. I wonder if her B12 reduction is the answer. Can anyone help?