A common problem with mouse whose scroll wheel stops working or works better in one direction or works intermittely. You google it and they take you on a wild goose chase...and you spend hours trying this and that solution and find out not one of them works.
Here's a much simpler solution and I am not charging.
You search google or youtube for "how to disassemble and clean "add your brand of mouse here". Mine is a logitech M510 so I am posting the video for it.
Tools needed: tweezer (ask your wife if you don't have one), a small screwdriver ( I mean thin ), preferably magnetized so it can pick up the screw after you unscrew them. Magnetized screwdriver are more helpful when you are rebuilding the mouse. A toothpick to access spaces around the wheel that the tweezer can't access.
First shut down your computer. Turn off the mouse and remove the batteries.
To begin with, you don't really need to take the mouse completely apart as advertized on the video. Just the two screws (for my brand of mouse) and be gentle when you pull on things.
Pay attention to how you removed a part. If you pull on it, you would have to push to get it back in. If you slided the part out, you would have to slide it back in. Don't force the parts to fit together.
when you take the mouse apart, you will be surprised by the amount of dust packed around the scroll wheel. With the tweezer, you can remove most of it. Then you use the toothpick to remove the dust you could not remove with the tweezer.
In the end, you vaccuum your mouse.
Reassemble and you are ready to go.