I agree with PPs that your DH is scared. The threats come from that, and the car takes her further and further away from him.
I feel this. I have an 18 yr old and I'm really upset that it went so quick from being a babe in arms to someone who (might) call me to let me know which pub they are in and whether they are going to be home for tea (or at all).
We have a tracker. Everyone is on it. No-one gets upset. We did ring up the 17 year old at 3am once when we spotted he was in a very dodgy part of London when apparently staying over at a mates.... tracking to a bus stop for which service had finished many hours since... my DH may have slightly lost his shit that night... we were worried that poor choices might have been made, or that he was in trouble.
I have also changed the names of all the takeaways on out tracker to things like "You fat fucker" to help with DH's diet efforts... it now pops up as a message to say DH checked in at Greedy Bastard!
But back to the point. In out house we are all on the tracker. We use it to see when each other will be home for dinner, to check on whether the kids arrived safely somewhere... to help the 17 year old who DOES get lost... so we can immediately look him up and sort directions... to find lost phones.... and sometimes to check up on the kids when either myself or DH have an anxious moment. No one has a problem with it.
I actually dont think the app needs to be deleted. None of you have secrets.... I think checking every 15 mins is excessive and you should be thinking about what DH needs in terms of support for his anxiety. He is at risk of pushing his previous daughter away.
Please don't label him as a bully or an abuser. I think he needs support. He qyite likely still sees his baby where others see an independent young lady.