This sounds like a great project for an 8th grader. In answer to your questions:
1) I think it's perfectly okay to refer to the grease released from the chips as fat, as long as you have defined it that way earlier in your write up. You'll probably write somewhere "we measured the amount of fat in our chips by determining how much grease the chips released..." This should let anyone reading know how you are defining fat. Your daughter may want to be aware that this is probably not an accurate measure of ALL of the fat in the chips and be able to mention it as a potential limitation of the experiment, but for labeling purposes and such, I think you're fine.
2) In general, for your graph, you wouldn't label the axes as x-axis and y-axis or "Independent Variable" and "Dependent Variable." You would label them as what you actually looked at/measured. So in the case of your experiment I am envisioning a bar graph where along the bottom (x-axis) you have the different kind of chips (each type of chip tested will get a bar), and on the y-axis you have the amount of grease released (as measured by the number of squares on your graph paper were saturated by grease). You would then label the x-axis "Chips" or "Types of Chips" and have the type of chip for each bar graph, and you would label the y-axis "Amount of Grease (or Fat) Released." It's also common to have a unit of measure included, so in your case that would probably be "Amount of Grease Released (# Squares)" or something like that.
3) See the following link to a page we have on independent and dependent variables to help explain them further. http://www.sciencebuddies.org/science-f ... bles.shtml
In brief, the independent variable is what the scientist is changing, and the dependent variable is what the scientist is measuring. You are changing the type of chip, and measuring the amount of fat in each type of chip, so I think in your previous post you had the independent and dependent variables switched.
I hope this helps, and that preparing the board goes well. Feel free to post again here if you still have questions on variables or anything else comes up.