Not really an option, when the data is being used for billing purposes (which phone, used what services, and when).
The US has no laws forcing data retention like the EU, but it would take something like anonymous micro transactions in order to have a working billing system, without collecting the data (and it being available to law enforcement).
That’s going to be a “he said, she said” case. Chances are, since she was an activist in the US, that she might’ve been labeled as an “instigator” in whatever ID database they are using.