Did the extended trailer ruin this scene?

There's more to the movie than her tragic death, and it's probably going to focus mainly on the father/son relationship as well as their fight to survive and save the world, this is my guess. If it was a part of the plot that's meant to be hidden, they wouldn't have thrown it out there so blatantly, IMO. 

Believe me, when we see Godzilla fighting the Mutos, this scene will be quickly forgotten.

I feel like you guys are missing the point. I'm not saying it's a big part of the film, but it could have been a very tearjerking moment had I not seen the whole thing prior to the movie's release due to a trailer. 

I think specifically what will make the scene touching will be the specific dialogue that they share.

The fact that they die in and of itself isn't moving. There are meaningless character deaths (even of main characters) that lack emotional weight all the time. And this particular trailer didn't even spoil the fact that she was going to die. We already knew that, because as you mentioned, most people figured that out in the very first trailer in December. 

Seeing as the death wasn't a surprise, and how the emotional level of a scene is largely dependent on how the scene is crafted, rather than the fact that the scene merely exists, I really don't think this most recent trailer spoiled or ruined the scene any more than it already was by previous trailers.

On the other hand, letting people know that there will be some emotional depth by teasing this scene is a great way to let people know that this movie isn't just Pacific Rim 2. It's a great scene to show to entice non-Godzilla fans to see the film.

For example, my roommate (who hates Godzilla, but likes Breaking Bad and Juliette Binoche) watched this trailer, and afterwards said: "Well this movie doesn't look like it's going to be as bad as it could be"....which is a HIGH compliment coming from them given their previous disposition, and means they probably will actually see it. This change of heart definitely didn't come from seeing Godzilla roar or seeing the MUTO's claw. I'm 95% sure it came from seeing that scene in the trailer.

Besides, I feel like there will still be weight to this scene to be experienced in theaters that the trailers haven't gotten to yet. 

That all being said, I do hope that other than POSSIBLY the 2013 Comic-Con trailer, that they stop releasing new footage. I'm more than satisfied with what they've released so far. They've put together a great package to pitch to people with what they've already shown. The key now, I think is shift gears from showing off new stuff, to showing that stuff to more people. Awareness, rather than content spoiling needs to be the key for the remainder of the marketing. The content will do a great job selling itself, it just needs to be seen!!!

For me it's the buildup for the scene and that makes it. Now I know all the precursors for how this happened. I see scene for scene basically of him having to be the 1 to trap her in there( a scene that would have been been left out) Knowing that she was going to die didn't really matter but actually showing it was him closing the door in a preview was just too much for me. That would have been a surprising moment at the theaters, but now I feel it's ruined and sure I have their dialogue but 1 can roughly guess how that's going to go now that we've seen so much. Basically him saying he's sorry and he loves her and her something along that line of take care of the kids ect. Just a little less of the scene would have been so much better. 

Of course this is all my preference but I feel the trailer crossed some lines in that particular case.

I absolutely agree that they shouldn't have showed as much as they did. That being said, you have to make the general audience want to go see it. All those shots will not feel the same- the one where Brody is screaming down the hallway into nothingness as the radioactive cloud approaches him, the touching circle window scene- yes, they will not have the same effect as if we saw them for the first time.

However, we also have to think about the fact that we won't have much time to gather all the emotions as the power plant is literally melting down. The trailer already sets the sad tone so we're ready to grab all those extra emotions that we probably would have overlooked if the buildup by the trailers hadn't been set up. But I do agree, they should have shown less.

Yes, most undoubtedly!