Kate,
I'm getting married at Lindquist. There's pros and cons of both Lindquist and Magen's. Magen's is pretty and has bathroom facilities, etc., for guests but tends to get very busy(especially on heavy cruise days). Lindquist is more secluded, no bathrooms, but a lot less people.
Does she have a coordinator? I think there are probably shaded areas on both beaches. I know Magen's has those two big palm trees a lot of people get married between. Also if she had a late morning ceremony (like 10:30) she wouldn't have to worry too much about the sun.