It is, in light of the revelation that the OP has made the cardinal error of also impersonating her sister on the phone and incriminated her in the process. It is only because TfL now have cause to believe the sister knew the pass was confiscated that the course of action should change.The only appropriate response to the OP is that they tell the absolute truth and own up to their mistake.
But the advice by people in light of the information previously, that her *sister* had been written to, and that they’d no idea who the OP even is, nor even accused them of an offence, was certainly not sensible at all!
You do not need to do the investigators’ work for them, especially with them having written to someone they know for a fact wasn’t the person stopped. This forum is for advice, not a moral posturing ground for people to suggest always cooperating fully - to the point of wilfully incriminating themselves - even when it might not be in their best interests.
For the record, nobody has advised anyone to “circumvent” any legal process, not that any such thing would be possible anyway.