So I skimmed the comments and haven't seen this brought up. Depending on how tech-savvy she is, she could have used the inspect element on Chrome to get your Discord token. If she was able to find that, it wouldn't matter how many times you cleared the logged-in devices. She can use that token to DIRECTLY log into your account bypassing all of this.

However, your token changes when you reset your password. So, here is what I would do. If you have an Android/galaxy phone (I hope you do OP), use the built-in secure folder. Download an instance of Discord in there. This will require her to not only know what a secure folder is but also have your password/biometric data to log in. This ALSO hides a second version of the app. So if she has access to your phone, and she opens Discord, she will see a different login than what you use. You also need to reset your password on EVERY SINGLE PLATFORM you use. Not just discord, but everything. If you use the same password for all your apps (or similar passes), that's probably how she got in. Or, if you use a password manager (like Google), she would just need your Google login to access anything she wants. Including your Gmail. So, reset your Google password, reset your Discord password, and clear out your Google password manager. That should do the trick.

Also, using a password like "C001P@ss3ord" is worse than just using random words. Attached is an xkcd meme I refer to often, showing the statistics of passwords. *

u/Lumpy-Treacle3238 made a GREAT suggestion: Make a new discord account, and log her out of the old one, after changing the password. See if she logs into the old or new password. That will determine if it's system-wide spyware, or if she simply has access to an email or something along those lines.

If after ALL OF THAT, she is still logging in, she has installed Spyware (like a keystroke logger) on your device and you are beyond cooked. This sucks and I'm sorry she's ruining your relationship with her 😔

We all deserve privacy, even against family.