If she's competing under IJS (which I guess she is if she's doing the Lee Valley September event) then to understand how the scoring works, there's a big helpful table of how judges mark the elements here:
http://sk8stuff.com/traindocs/5_levels_perspective.pdfSo to answer your specific question eg. a plain base value single toeloop is worth 0.4. If it's really good, it'll get +3 grade of execution, which is another ).6, total 1.0
Meanwhile a double toe is worth 1.3, but -3 GOE would knock 0.6 off it, total 0.7. So at the extremes, the good single is better. But I think you'll rarely see +3GOE at lower levels.
To understand what makes a jump "good" for GOE, scroll down in that document to p10 for the jump bullet points and you'll find height, extension, flow and several other things.
Hope that's helpful. That document only covers the technical elements side of scoring, there's also scoring for skating skills, transitions etc, which is even more complicated!
Good luck to your daughter!