Cheeseheadsaint: Sorry, but I've got to come down on the side of your friend here. You may have provided a lot of coaching and technical support both before and after, but the inescapable fact is that when it came to actually taking the picture, she did it.
Look at it this way: out of a near infinite number of choices in that mystery we call time, she decided which 1/60th of a second to extract and freeze forever. No one else did it. She did it. That's why it is called "The Decisive Moment" and she was the decider.
Pancakeman: In the U.S. the law is pretty clear. The employer owns the pictures. If you are in someone's employ, their rights can even extend to your off-time (although few employers push it that far). Your software example is a classic example.
So, why don't the bride and groom own the wedding pictures? Because the photographer is not their employee. They hire the photographer as an independent contractor and the terms of the contract govern ownership, etc.
Cooperative agencies like Magnum came about in order to protect photojournalists rights to the pictures. They use the agency and contractual relationships to preserve the photographer's rights.
Now, people can litigate almost anything and there are always nuances that can impact the situation. Best advice is to avoid it in the first place by coming to a reasonable agreement up front.