The current protocol for the interwebs is IPv4. This means the max number of unique addresses is 4.2 billion, less than one for each person. Think how many devices you have, different connections (mobile data, home broadband, work VPN, open Wi-Fi etc) and then realize how small that number is. I'd bet good money I can "guess" the address of people's internet router, because they mostly the same!
Trails are left by email addresses, and with the correct permissions you can work out the internet service provider used. If they cooperate, you can potentially get to a person. Anyone using open Wi-Fi, mobile data, VPNs will not be traced.
It's a good excuse to close down everything, restart. I know I said earlier I hope she changes, and that is true. But it's still true that needs to come from Jack and she needs to understand what she has done is wrong.