The bottom line is whether she sees the shot accurately. Have her play short straight-in shots and see if she lines up along the correct line, with the cue stick pointed through the centers of both balls. If she doesn't have that part right, I think it is the first thing to work on.
I'm left eye dominant and right handed. Much of what has been said above does not apply to the way I aim or my perception when shooting. I was unaware of the issue for the first 15 years or so that I played but then a friend asked me why I always lined up on the left side of the cue ball. I was over sometimes as much as a whole tip but it looked like the center of the ball to me. Yes, I could be off that much and it would still appear to be the center. I had subconsciously learned to swerve from left to right on the final stroke to hit the cue ball in the middle.
I wish I had had access to an instructor who knew what he was doing back then, but I don't think fundamentals were really understood or taught very well in this country in the 1960's. Just a video would have helped with the diagnosis, but the technology was not there yet.