If she has $350, buy one of these and do DIY. And she can check on a regular basis.

https://www.amazon.com/Spy-Hawk-Security-Products-Pro-10G-Detector/dp/B00LZFD3XA

My wife has one from when she was traveling all the time.

@Tropical_Willie, thanks, I’ll forward the info!

Call a security consultant firm and ask.

I am betting Lucky Guy might be able to answer this one.

Also, have her check her phone. So many people set up find my phone and give access to it to family members or boyfriends and it makes it easy to find you as well. Airplane mode is the easiest way to stop this but then it’s no good to use. So she should look for this app on her phone and shut it down. Also if she ever shared an app like Waze and they share the account then he can definitely see where she is. Just in case she’s not aware that they share an account, I would have her delete the app and sign in under a new account with a different email. I think it’s more likely he’s following her phone than her car.
Also, make sure he’s blocked from all her social media and his friends need to be blocked as well. If she has her own friends that are still friends with him they need to block him or she needs to block them.

Once she is sure that he’s not able to track her she should tighten security at her home. Get a camera.

@Pandora The phone has already been established as clean. She is specifically wondering about the car, for a few reasons.

Does the boyfriend have access to the car? If yes, then there is the possibility that the bug is magnetically mounted in an easy location so he can retrieve it and read the data later. She can ask her neighborhood garage mechanic to spend an hour looking carefully for things that don’t belong.
Unfortunately, If it is a sophisticated tracker there is very little chance it will be found.
Her phone my be clean but he might have her password and can access her location history regularly.

Also there are modified Onn trackers that run for months on Android, and Apple AirTags that run on IOS. The devices are modified so they don’t alert the user. It is very difficult to find one of those. Slip one in an air duct and it would take forever to find.
If possible, use misdirection to foil the tracker. Examples: Trade cars with a friend. Park the car somewhere else for a day or so. Leave your phone at home. Park the car at a hotel, etc.