Turns out, all I had to do was wait. I've just found scans, not only of Sun Girl #2, but also several issues of the wonderfully bad Moon Girl*, and even Venus. I'd love to get these in actual paper format, as I did Fantomah, but no one seems in any hurry to reprint these gems.
Sun Girl #2 is a nice little comic. It's not Earth-shatteringly exciting or significant, but honestly I'm a little sick of how every comic needs to be part of some cosmically important event lately. The art is full of character and wit, if seeming a little cramped at times, though that may just be the result of it being a more compressed level of storytelling than I'm used to.
In thirty pages we get three Sun Girl stories, one Blonde Phantom, and a text story. Sun Girl fights electric aliens from another dimension, thwarts a pair of burglars by laughing at them, and defeats a horde of crystal monsters, while Blonde Phantom solves a crime that she knows nothing about.
While not quite up to the high standard of issue 1, it's light and fun, and I only wish the series had lasted more than three issues.
*Though bizarrely, someone seems to be doing a new Moon Girl series. Who on Earth thought that was a good idea?