My mother is also not a classical "good" mother but not as worse as your case.
Try not to "calculate" what you have given out and why she didn't appreciate. It make things worse.
From my point of view, it's time for us (grown up already) to contribute ourself and to care and to satisfy them (the mother who's getting old), no matter how bad she is.
And in your case, is your mother's behavious abnormal in other ways. I mean, even when she treats other people? If you suspect she has "emotional problem", try to help her instead of stepping on her any more.
Sorry that it's much easier for me to type English.