In the past, I've put my hand out like a stop, then said I really have a few things I need to talk about today and don't want to run out of time. Then, I started each session by telling her what I wanted to work on and asked her to help me keep the session on track. That works fairly well for me. She still rambles occasionally, but I'm able to tell her that she's talking too much.

A previous t was a huge talker and I ended up quitting. Actually, I got up and walked out while she was talking and never went back. This was after my bringing up her talking too much and me not being able to work on anything in session, so she had a chance to change but didn't. Good luck