The problem is that people claim that their emotions are "theirs", but can't choose not to react when they feel them. Without emotional control, the emotion isn't owned. And emotions are responses to perception, so they will feel something, even if it isn't a valid thing to feel - so people respond to a misunderstanding, as if the reaction is appropriate, even when it is not.
There is definitely a difference between repression and control. Yet, the people who aren't willing to learn control, aren't willing to admit the difference.
Exactly, a person can't fully own his or her emotions if he or she can't control them; rather, if he or she lets his or her emotions control him or her, then it is like letting one's emotions own himself or herself.
As for explaining to her the difference between repression and control, it's truly hard since she's probably one of the people who failed or chose to fail to see the difference between those two.