Take the tracker and put it back on her own car without her noticing Then that way she would be following herself everywhere trying to find you

It's illegal to have spyware and use it on someone without their consent.

If she has had access to your phone, like asking to borrow it to make a quick call, double check to make sure she hasn't downloaded any apps and hidden them. There are seemingly innocuous apps you can download on someone's phone without them realizing it that can allow them to track you, read your texts, see a list of all your phone calls, etc. Maybe it's just me being paranoid, but I found out my, now ex, boyfriend had done it to me after coming across a hidden download that was named "Settings" and was identical to the real Settings widget. Your MIL obviously has no regard for your privacy, so I wouldn't put it past her.

What an opportunity for some fun! Let her plant the GPS tracker. I'm assuming that she'll track the GPS via computer at home Remove it. Go and put it at a brothel for a few hours. And then a jail carpark. Maybe outside a drug rehab place for a while. Don't forget the abortion clinic. Even better, get a friend to do this... whilst you're with your husband. The Mother-In-Law will go nuts and make accusations in front of you and husband... and husband will know she's nuts because you were with him at the time. Game, set and match!

I would have kept quiet and let her do it and then remove it and put it on a random car.

Check your husband's car too.

Errr maybe it's time to write Dr. Phil...

Rabbit stew

Should've allowed her to put it on, then that's when you ship it to a different country.

wait till she puts it on, and while you are driving, park somewhere, take it off, and stick it under another car :)