Speed will not make a bit of difference for her. We are talking 15 yards, 45 feet, meaning if the arrow is moving at 200 fps its there in .255 of a second, now go out and shoot at 300 fps and it gets there in .150 of a second making a difference of .105 of a second.
Here is what I recomend, stop trying to shoot deer over a NJ bait pile, they are obviously on alert from pressure and scent. Move to a new spot free of said pressure and she will be fine. My wife shoots a Parker Sidekick that is "slow" at 45 pounds and had zero problems killing a deer a couple of years ago. It ain't the bow.