The g'moro in psochim 2b says that a father who goes to rob his son, will not kill him and therefore if the son kills his father he cannot claim self defence. What about if a mother goes to rob her son and the son kills her, can he claim self defence if he kills her.
Mabit (vol. 1 ch. 339) writes that this applies specifically to the father; not to the mother. However the Gemara Sanhedrin 72b writes that anytime that one knows that the intruder is a very close beloved friend who wouldn't harm him, then he cannot kill him, so Mabit would agree that if one has such a relationship with his mother then it would be forbidden to kill her. Mabit is here