Margaret Macomber's intentions and actions

Earlier in "The Short Happy Life of Francis Macomber," it is shown that Margot doesn't like her husband partially because he isn't excelling at his current activities (which was most of the purpose that she married him, the other part being the money), and also because she doesn't love him as a person, especially at that point of the story.  Near the end of the story, it is apparent that Margaret had jealousy and fear regarding Francis once he finally realized how to not be afraid of "hunting", which includes not only taking charge of the animal's lives, but also taking leadership over certain situations with humans.
It even says from Francis' point of view that Margaret "was very afraid of something."  She even acts tempered, making bitter and impatient comments such as "isn't it sort of late?"  The last that Francis saw of his wife before he got killed in action was when he waved and did not get a wave in reply.  During the encounter with the buffalo, it was unclear what killed Macomber, although it appeared to be the buffalo.  This may have been the case, but I think it more likely that Margaret did kill her husband, whether or not it was by accident or purposefully.  Since she was going through a tough time emotionally then, she was more likely to pull the trigger.  I believe that it was a gut reaction because she saw her husband being charged at, and even though she didn't particularly like him then, she still didn't want to let him die doing what he had begun to like; It was probably an accident, and although the shot was supposed to hit the lion, it hit Macomber because he happened to be right next to the lion.  This reminds me of a scene from the movie Soylent Green where an assassin tries to kill the detective with a gun in a large crowd and keeps hitting other people instead of the intended target.  At the end of the story, she just keeps repeating "stop it," which Francis was probably thinking throughout that story, and also because she already feels bad enough about what she did, and doesn't want to think about it anymore.