talking to my mother

Laura
So my husband and I moved on with my mother a few months ago. The main reason for the move was because she's struggling and not able to really work much and her house is a disaster. She simply cannot take care of it herself. She lost my dad 14 years ago and since then has just piled things into the home and let the house itself go. We talked and I would love to raise our future children where I was raised. 
So here's the issue.
Every time I talk to my mother ( or really anyone for that matter ) she just starts talking over them and steamrolling the conversation. You could be talking to her for five minutes straight and she just comes out of.l nowhere with a completely different conversation ( whatever she was thinking about) and just talk over you until she's done talking. 
This is incredibly frustrating. Not to mention she's been pissed off for the last 14 years which she has a good reason to be but she's just pissed for the sake of being pissed. It's so hard to live with her. I need to have a conversation about the talking issue, the always being pissed and bitching issue, and the we are he to help not take over issue. 
How do I do this? 
I've always been kind of a pushover from growing up like this. 
Any advice would help!