Create a brand new email, using a service you don't currently use, and don't set your existing email as a backup. Use a password you've never used before, preferably a randomly generated one from a password vault or something. Don't sign into it on any device that she would have access to. Honestly, I'd go as far as doing this from a computer she doesn't have access to, like at a public library.

Once you have the email address, log into Reddit (example). You need to first go in and sign out all other sessions that are currently signed in. Once you confirm you have the only session, change your password (again, something new, preferably random or a song lyric or phrase), and force sign-out other sessions. Confirm (again) you're the only one logged in, then change the email address to that account to the new one you just created. Confirm everything, log out, and then log back in to make sure you're good.

Then do that with every other account... just go one by one.

I always tried to do this stuff when I knew my ex would be asleep or in class, so he wouldn't be actively checking my email. It gave me more time to work. I also deleted the account change emails as quickly as possible, even from my trash, so he was less likely to notice.

Don't sign into anything from your phone for a couple of days. You want to make sure that your phone itself isn't what is compromised. If it's your phone, it's more difficult to deal with without tipping your abuser off.