The referee notes it takes trainer Amy Baer two minutes to put McBride together again. The referee adds two minutes onto the end of the 45-minute half. An official lets the crowd know the amount of stoppage time by holding a message board on the sideline between the benches just before the scheduled end of play. Note that the scoreboard clock does not run past 45 or 90. Only the referee knows how much time is left.
Discretion is exercised.
You could watch a hundred matches and never see action stopped while a team has a good goal threat. However, if a team is in a non-threatening position, the referee will stop the proceedings once the allotted stoppage time has been exhausted.