Cases that are reported are generally sparse on detail.
Some don't mention any reasonable cause 1 2 any most mentioned some kind of criminal distant past, 3 , 4
The stories are also disproportionately about Colombians, Mexicans, Filipinos...Most European's who got into issues were not GC holders but messing around on the wrong visa (e.g. working while on ESTA).
If you don't have any kind of criminal record, then as a UK citizen with a GC your risk will be very low.

You are technically correct, however there is a distinction between "rules" and "discretion", and we have veered sharply in the direction of "strict enforcement of the rules" when that has the desired consequences, which appears to be "media perception of being tough on immigration".

If she doesn't want to reside in the US and hasn't attempted to become a USC after all these years, then becoming one doesn't make sense. The green card status will eventually lapse and USC means she will have to pay or at least file US tax statements.

I desperately want to return to living in NY but know that if I could afford it, life would be completely different from what I left behind and probably totally distasteful.

The OP should just travel and return to the US after her trip on her green card. As long as she doesn't have a criminal record/history, taxes are current and she has a home to return it, she will be fine.