Windows 10 mouse won't let go

When one of my windows 10 users opens our web design interface, her mouse starts acting weird.

In the middle of one of the screens there is a text box that you can resize to make bigger. There is a gray triangular button in the corner of one of the windows that lets you resize the window. For the rest of us, you left-click that button and drag to down to make the window bigger. When you lift up your finger, the window size is set where you lift your finger.

When she left-clicks and drags to resize the window, the mouse won’t let go when she lifts her finger. It’s like her mouse won’t let go of the resizing button. As a result, wherever she moves the mouse the window resizes. She has to fight the mouse to let go. (I suspect it’s making her double-click to let go.)

I’ve tried several google searches to find the answer but I don’t think I’m using the right syntax because so far I haven’t found anything that rings true.

I’m going to try to disable “Scroll on inactive windows” but that’s just a guess. Any thoughts?