If she is consistently getting facts wrong in her oral narrations, I would probably scale back on the length of the reading. Once she shows consistency in paying full attention at the shorter length, you can start adding to the length little by little. We don’t want to reinforce a habit of inaccuracy.
If words are missing in the written narration, it sounds like she may be hurrying through rather than paying full attention and doing a thorough job. Shorter passages may help with that aspect in writing too.
As far as how long to focus on an aspect, I’d recommend you continue to keep track of how many times an infraction occurs in subsequent narrations. (And by the way, make sure she knows which aspect you’re tracking, so she can work on improving in that area too.) Don’t wait for perfection before moving on, however. When you see consistent decline in the number of infractions—or consistent improvement in that aspect, if you prefer to think of it that way—add the next aspect and hold her accountable for both.