I don't know if this will be of any help, but I'm 5'1" and wear a size 9 1/2 ring currently. I weigh 250 pounds, which is a lot more than the 175 pounds originally suspected for Princess Blue based on the ring size. Someone of her height of 5'2" with a 9 1/2 ring would either weigh well over 200 pounds, or possibly have a large knuckle and need an oversized ring to pass comfortably over it. My guess is the same as most of yours, though, that this was not her ring.
I did want to mention that she may have used a pad to make the ring fit -- the girls in my high school in the 1980s used bunion pads to make their boyfriend's class rings fit!
My high school ring (a size 7 from when I weighed 120 pounds) was also from Jostens in 1990 and looks nearly identical to Princess Blue's. Her ring is most definitely the girl's version of the Jostens ring, no question. My husband has a 1988 boy's Jostens ring and it is much larger. You can see examples
here.