How to tell a person to stop oversharing things

My flatmate shares with other people everything that's happening in the household including stuff about me. She doesn't do it on purpose, she is just a talker and does not filter most of the things when talking to other people. I noticed that she tells me everything about what other people told her without missing a detail and once she shared with the guest a detail about me which I prefer to keep a secret but I have to tell her since I need to make an arrangement in the flat (calls, meetings). I don't want to come off rude but it's disappointing that some people don't realize that blabbering everything without putting a filter on it is an issue for their surrounding (she shared with me that our acquaintance has a disability tho I think it's not okay to share such a private information). Since she shares with me everything, I assume she also shares with others everything about me