shades said:
And...the same sun sensitive people still have to walk around the park with no shade - and some will spend full days in the park???
That is true. It's sort of the same idea as WDW's suggestion that someone with an endurance problem should consider a wheelchair or
ECV because the time spent walking around the parks is much greater than the amount spent in line.
My take on the "sun GAC" (and this is IMHO, not any knowledge about policies, etc) is that it's for those situations where the person either is not able to use the usual ways to avoid sun exposure (which may be the case with the OP's DD) or the usual ways are not enough to prevent having problems with the sun (which is sometimes the case for some people with medical problems/certain medications).
The "sun GAC" is sort of up to the discretion of the CM at the attraction. I don't know what the stamp currently says, but it used to say "a place to wait out of the sun when the queue is in the sun for a considerable length of time."
That leaves a lot of "grey area" for exactly what is meant (ie, what is "in the sun" and what is "a considerable length of time"). How they handle it would depend on what it available at that attraction - they could have the person with the GAC and one member of their party wait inside the shaded area of the attraction until the other members of the party (who are waiting in the line) get to them. They may have your party stand aside in the shade for an amount of time equal to the time you would have waited in the unshade part and then send your party into the line.
As was already noted, most of the lines are shaded, so you usually are not actually in a line a very long time before reaching a shaded point. If you are going at a slow time, you will experience short waits and actually may not wait in the sun at all because you will enter the line where it's already shaded. All of the Fastpass lines (at least all I can think of) have sun covering or are inside of buildings, so using Fastpass is one way to avoid sun exposre.
People might think that they could use this GAC to go in the Handicapped/Wheelchair viewing areas, but many of them are smack in the middle of the sun and not shaded at all.
Another thing to consider is using sun protective
clothing rather than sunscreen. A few years ago, there were only a couple of companies, now there are many. Here's a
good article about sunscreens and protective clothing. It does make the point that there are no specific guidelines for clothing sun protection claims, so look for things like endorsements by Cancer or Skin Cancer societies and how long the company has been around.
Here are some links to sun protective clothing (in no particular order):
Coolibar
Sun Precautions
Solar Eclipse
Sun Protective Clothing
Skin Savers
Sungrubbies
Sun Clothing, etc
Sun Protected
SolarTex (from Australia)
stingray
Sun Solutions
This company seems to have much more selection of sunscreen than most:
Shady Lady
It would seem to me that other disabilities would have to be involved -because there are lots of people who would fit this category. And...the same sun sensitive people still have to walk around the park with no shade - and some will spend full days in the park??? I just don't get it.....no disrespect toward those asking the questions or anybody needing some assistance - but, there just has to be more of a requirement than being fair skinned and sensitive to the sun. 
