The correct answer to this open question is the following.
Unfortunately, you did not provide any context or background about the situation of Sally and the problem with her slides. We do not know it, just you.
However, trying to be of help, we can comment on the following general terms.
When someone does not meet professional expectations, this means that this individual did not prepare her presentation, lacked technical skills, did not included proper sources, or missed the proper visual aids to make the presentation more attractive and dynamic.
What Sally can improve about her slides is the following.
She can design a better structure for the presentation to have more congruence.
Sally has to clearly establish the goal or goals for her presentation.
She has to add many visuals instead of plain text. This way she can better capture the interest of her audience.
If she can use more vivid colors instead of pale or dark ones, that would be best.
No paragraphs unless necessary. She better uses bullet points.
Take care of the tone of her voice. During her practice, she can record her vice to check how it sounds.