To build further on Julie's
godsend, you could say
The cop arriving was divine intervention.
When a miracle happens. When the hand of God reaches down and saves someone from a life threatening or dangerous situation. (UD)
When someone is placed in the right place at the right time to be a catalyst for someone in need, when the person in need may have been in angst about how they would get through a certain situation.
Surprisingly, Urban Dictionary is the only citation I could dig up.
Along the same lines, you can say that it was Providence.
Providence is the guardianship and care provided by a deity or god. Religious people thank their god for his providence. (Vocabulary.com)
The word provide is a good clue to this word's meaning: when a religious being is said to give people providence, he's taking care of them — providing for them. For religious people, any good thing that happens to them — like landing a new job, getting healthy, or finding money on the ground — could be considered an example of providence. You can also talk about people providing providence, if they're showing care and prudence in managing resources.