Is there any reasonable explanation for Christiana Pedersen's ...?

This is an answer in full referee instructor mode, and it will be long in order to give a full explanation.

We first need to look at the LOTG and their interpretations by FIFA and the IFAB (the International Football Association Board, the body which makes the rules). Law 12 states that the goalkeeper is not to hold the ball longer than 6 seconds before releasing it into play. The sanction for doing so is an IFK. The 6 second rule replaced the old 4 step rule in the late 1990s.

However, the interpretations by FIFA and the IFAB are clear that this offense is not to be called too closely. What the referee is to look for is not just if the keeper has gone over 6 seconds, but rather he is to analyze the keeper's action to see if he is intentionally wasting time (this was a major issue in the many boring games of the 1990 World Cup).

Unlike, for example, a shot clock in basketball, the referee is not to be counting the seconds and calling the foul as soon as he passes 6. The purpose of the rule is to make sure the keeper is not delaying the game. As long as the keeper is making a valid effort to put the ball back in play, the referee is not to be concerned if he goes over by a few seconds.

Additionally, even if the referee feels the keeper is deliberately wasting time, the keeper is to be warned by the match officials prior to the offense being called. The keeper should be given several warnings before the offense is called, as the sanction for this offense (an IFK inside the area) is steep for what on the surface appears to be a minor offense.

Because of all that, one can see why this offense is rarely called. It usually just doesn't apply due to the "valid effort to put the ball back in play" standard. Even when the keeper is delaying, almost all keepers (including, every keeper I've warned about it) stop delaying when warned.

We must now look at the game in question, and see how the above applies to this specific ruling. Watching the game live, I was shocked at the awarding of the IFK. The referee had been long struggling with with foul recognition by that point, and I was initially flabbergasted by the 6 second call.

After a full analysis of the match much later, however, I would have to agree with the referee on that call. I had been watching the game more as a fan than a ref, and had missed the delaying done by the keeper. Not only had she been taking a long time, but she was indeed not making a valid effort to put the ball back in play quickly on many distributions.

Additionally, we have learned that the keeper was indeed warned by an AR about her delays (which does count as a warning, even though it didn't come from the CR). That part has been admitted by the keeper. While we have not heard directly from the ref (and probably won't due to FIFA policy) both her father and Abby Wambach said the referee also warned the keeper several times in the second half (definitely not unbiased witnesses, but Wambach did admit to her attempts at gamesmanship in the incident, which gives her some credence).

Consequently, it seems that all the requirements for calling the 6 second violation were indeed met. Again, its indeed rarely called but not because its not supposed to be called if warranted. Its rarely called because it usually doesn't apply because the keeper is not truly delaying, and because those who delay usually cease doing so when warned. It appeared the Canadian keeper continued to delay despite being warned.

Another, although indirectly related factor, is time wasting. Referees use a number of different criteria to judge time wasting (note that in referee terminology, there is a difference between legal use of time, and illegal wasting of time). A major factor considered is if a delay is being done by the winning team late in a close game. In this case it was a 1 goal game at about the 80 minute mark.

On a final note, I mentioned earlier that the ref struggled with foul recognition in this very physical game. This is simply conjecture, but since many hard fouls were going unpunished, the Canadian keeper may have simply thought the ref would never call her for the delays, even after the warnings.

Edit based on additonal details: I wrote 3 more paragraphs, but the answer was rejected for being too long. In a nutshell, you are incorrect about both the letter and spirit (both were followed) and the yellow card. Solo was not in violation (although she was the last time I saw this called, in a 2009 pro game). A card could not be given under the circumstances for time wasting. Read my answer again and try to think about it. Stop thinking like a bitter fan, and you will see the answers.

Then you haven't been looking very hard. It was addressed on Yahoo! Answers in at least 3 places in this section alone. There are also referee forums that explain it.

In short. This is a rare call that is generally only called after repeated offenses, warnings, and more offenses. It has been demonstrated conclusively that McLeod (the Canadian goalkeeper) was, indeed, consistently taking 10 to 20 seconds per possession to put the ball back into play in the first half. She was warned at halftime to stop doing it. It continued in the second half and was eventually called.

Edit: Here is a match. Guess who the goal keepers are? Solo and McLeod. In this case, Hope Solo gets an IFK against her for delaying (see kick at 1:10 on the video).

http://www.youtube.com/watch?v=rafxT0zNQ4I

This is the match that taxreff mentions, I believe.

It's a rare call, because most keepers stop doing it once warned. McLeod played with fire.