What a nasty attitude from the doctor. yeah she may need to loose that weight, however isn't he listening to you that why all of a sudden she is loosing weight if she has changed nothing about her life. I would first start with a t-4 level this is her thyroid she may be HYPO thyroid. it may be nothing and it might be something more serious.
if there are more then one doctor in this practice then I would ask to see soemone else or else go back to her doctor and say you want to start to rule thing out do sonme blood work.
i think your mother needs to find another dr. this does'nt sound right if she has'nt changed her eating habits. take care. remar