Is there such a thing as coincidence?

Of course.  Or not.  It all depends on your philosophical or religious leanings.

The truth is, they happen all the time.  Explain them as you wish.

Example:

Heather is on her way to Houston to see her father.  She happens to stop at Galveston on her way.  She happens to take a walk on a fishing pier.  She happens to meet the very guy who was working at the pier when her mother was killed there ten years earlier.

Wow.  That’s a big coincidence.  Almost unbelievable.

But what if you knew early in the story that Heather knew that her mother was killed on a fishing pier in Galveston.  And that there are only two fishing piers in all of Galveston.  And that she stopped in Galveston for the very purpose of finding that pier. It goes from coincidence to purposeful event.  What about the guy at the pier?  Well, Heather knew his name because he provided eye-witness testimony ten years earlier.  He didn’t just work at the pier, he owned the tackle shop that operated on the pier.  An internet search told her he was still alive living in Galveston.  The odds of him working at the pier on the day she shows up?  Yeah, that takes a little fortuitous timing.  But stranger things happen all the time.

The key is foreshadowing and structuring the story in a way that dumb luck is taken out of the equation.  Be careful with coincidence.  Your credibility is on the line.