Obviously hard to comment as no full details yet, but ...
Assuming an individual complained to the Police, who responded by talking about arresting her, they are going to be on dodgy grounds.
Assuming it is the leaflet of the PoW they are interferring with a candidate canvassing as part of a GE.
And a party that is officially registered.
So even if it was a usual suspect being vexatious, you would have thought that by now the police would hesitate and think instead of the usual knee jerck response to a TRA complaint.
Can a complaint be made to the Electoral Commission?
Doesn't Sheffield police have a history on this - although on reflection isn't it Leeds where the police are the lap dogs of the TRAs?