First, I'll address the bolded part.
I don't think they should always spell everything out for us in movies. In this case I like how they did it, if it is what the movie may be implying at one point. And if so, perhaps next time people will think twice about jumping to the conclusion that it's a stupid plot hole with absolutely no explanation when there seemingly should be one, and instead try to be more observant and look for answers in the movie.

Now, Rey may not be a stranger to Luke. Based on what the movie may be implying, she could be Luke or Leia's daughter. The former seems more likely though.

The answer to your issue may lie in a vision Rey had in the middle of the film. In it you see a flashback of her as a kid being left on the planet by someone, Luke's hand on R2D2, and then a scene where Rey is on the ground, and someone is standing above her, about to attack her, but Kylo Ren kills him and saves her. What some people speculate is that this scene may be from the time where Kylo killed off Luke's academy students, but spared Rey. This would mean that both of them may have been part of Luke's academy. If so, Rey's memory has probably somehow been wiped.
When Kylo was informed about "a girl" being involved in the early incident in the film, he reacts rather fiercly to it and asks "what girl?"
Later on, during their lightsaber duel, Luke's theme plays when she grabs Luke's lightsaber. And Kylo tells her that she needs training, and "I can teach you", she closes her eyes, and perhaps that triggered her to remember her training, and that's when she beats him.

All of this are stuff that the moviegoer is exposed to, not Leia. Why would she not be interested in going to see if her brother is there for herself? Or send someone from the rebellion, just like she sent Poe to get that map (btw, who created that map?).

First, I'll address the bolded part.
I don't think they should always spell everything out for us in movies. In this case I like how they did it, if it is what the movie may be implying at one point. And if so, perhaps next time people will think twice about jumping to the conclusion that it's a stupid plot hole with absolutely no explanation when there seemingly should be one, and instead try to be more observant and look for answers in the movie.

Now, Rey may not be a stranger to Luke. Based on what the movie may be implying, she could be Luke or Leia's daughter. The former seems more likely though.

The answer to your issue may lie in a vision Rey had in the middle of the film. In it you see a flashback of her as a kid being left on the planet by someone, Luke's hand on R2D2, and then a scene where Rey is on the ground, and someone is standing above her, about to attack her, but Kylo Ren kills him and saves her. What some people speculate is that this scene may be from the time where Kylo killed off Luke's academy students, but spared Rey. This would mean that both of them may have been part of Luke's academy. If so, Rey's memory has probably somehow been wiped.
When Kylo was informed about "a girl" being involved in the early incident in the film, he reacts rather fiercly to it and asks "what girl?"
Later on, during their lightsaber duel, Luke's theme plays when she grabs Luke's lightsaber. And Kylo tells her that she needs training, and "I can teach you", she closes her eyes, and perhaps that triggered her to remember her training, and that's when she beats him.