Measuring algae growth or death
I don't think it's wise to use a spectrophotometer for this experiment, as it is a total count, i.e. it can't distinguish between dead and alive cells very well, and so she might not see a clear difference between her treated and untreated algae. If she has access to a haemocytometer and a good microscope, then she can count the living cells directly, and calculate the cells/ml using a simple formula.

This paper has a nice overview of how to count algae using a haemocytometer, and if her species of algae can swim, then she would need to use the iodine solution mentioned in here:

http://weis.science.oregonstate.edu/files/weis/Protocols/Symbiodinium/Cell%20Counts.pdf

I hope this helps!