In the doctors defense, my mother claims her doctor tells her all kinds of insane things. Like she is to only eat bacon for breakfast. Yeah, a woman who has had a sextuple bypass is only to eat bacon for breakfast I'll believe your doctor told you that.

Setting aside the fact that my mother is a socipathic liar it's more likely the doctor told her it was okay to eat bacon at breakfast every once in awhile and she translated that to suit what she wanted to do.
I'm thinking maybe the same may have happened with the OP's mother. (but rather a misunderstanding then choosing to hear what she wants to hear)
Doctor:"It looks like you've put on a couple of pounds."
Patient:"You know I filled up on ice water on the way over here."
Doctor: "Well, that could do it."
Translation for doctor=Filling up on water before being weighed could show up as a couple pounds.
Translation for patient=Drinking ice water makes you gain weight!
Of course I have no idea if that's what happened but I wouldn't call a doctor incompetent if I didn't hear him say it myself.