How to disable a floating right arrow button that makes FaceTime calls

Question

My mom keeps accidentally FaceTiming me and we think it's because of a floating gray button with a left angle bracket on it:

I've been trying to help her remotely turn it off. She must have accidentally activated it somehow today, but she is unaware of how it happened.

Assistive touch is turned off (confirmed via screen share*). Nothing in control center is highlighted. I've tried searching for it on my phone to figure out what enables it, but I cannot figure it out. I have googled and all I find is suggestions to turn off assistive tough, but that is off. I don't even know how to google it. I've been trolling through assistive access, FaceTime, and phone settings and can find nothing related to that button.

What is this button and how do you disable it?

*UPDATE: I screen shared with my mom and had her go to settings > Accessibility > touch > assistive touch. It was off. I had her turn it on and a second floating button with a white circle appeared. I had her turn it back off and the circle button went away, but the arrow button remained.

Answer 1

Apparently, the ">" button did seem to have something to do with Assistive Touch, despite attempts to turn that setting on/off not affecting it. That was Apple Support's thought, but something was screwed up, causing that button to exist when it shouldn't, so they had me force-restart the phone and that made it go away. I.e. We held down the power and home button (iPhone 6s plus) until the apple logo appeared in the center of a black screen. Once it fully booted back up, the ">" button was gone.