Yes, sentence does seem short. There is probably more of this sort of thing that goes on than is ever found out.
I am puzzled by a couple of things-
(a)if the patient was a dementia patient I am surprised about the bit that said: When asked by police whether the doctor had assisted with her financial affairs, Mrs Belham told an officer: "I think she just helped herself." Would her testomony be reliable?
(b) if she was childless who were her grandchildren?