When you use Power point to give presentations, you need to mention the important points on the slides and then you explain them verbally in front of the audience. Usually introduction is mentioned on the first slide and then begins the presentation.
In this question, average no of points she should write on one slide is asked. So there are 2 to 3 slides given and 15 points are there in total that she needs to write. So on average she can write 5 points on each slide if 3 slides are taken. Though on if she writes introduction on the first slide, she can write 3 points with it on the first slide and then 6 points each on the remaining 2 slides. This is how generally presentation is given.