Okay so my very nosy cousin, I trusted with my Twitter account. She would tweet things I did not like and look through my things. I was fed up and told her to delete my account. She showed me that she did, off of the app. I believed it but later she laughed and I realized she had tweeted all over again. How can I revoke her accessing my account without her knowing. We both have iPhones. I have changed my password and she was never logged out automatically like other social media sites do.
You should be able to revoke access via the Web using by going into Settings, then apps. This article in the support docs goes through the process in more detail: https://support.twitter.com/articles/20170805#revoke-access-web
In there you should see "iOS by Apple", click on revoke access and this should log you out of all iOS device using your Twitter account.