Bipolar-
Manic depression, also known as bipolar disorder, is a common condition characterized by alternating bouts of depression and upward mood swings. According to the Davidson College Biology Department, manic episodes include symptoms of inflated self-esteem that can manifest as the need to impart knowledge through incessant talking.

ADHD
According to Dr. Edward M. Hallowell's book "Driven to Distraction", Attention Deficit Hyperactivity Disorder (ADHD) affects adults as well as children. People who have the condition tend to live their lives in extremes, one of which is incessant talking. Constant interrupting, blurting things out and talking about instead of performing an organized task are also indicators of ADHD.

I researched a little on line and my sister still sounds like ADHD. This talking only developed over the past few years. She doesn't listen to what I say, instead when I start to speak, she runs off on the topic with her own take on it and telling me what to do. I wouldn't say she was ever rude or intentionally trying to be rude. It definitely seems just off.

The case of my mother goes much deeper and more toxic, so IDK.

Anyway, this is a very small annoyance in the grand scheme of my overall issues.