I once bought a Supergirl figure to customize into Stargirl - turns out I needn't have bothered.
The niece of S.T.R.I.P.E., Stargirl is growing up into a crime fighter to be reckoned with. She calls upon all of her training, and the cosmic power of her Star Rod, to fight foes from the streets of Metropolis to the jungles of Skartaris!
Stargirl was created by writer Geoff Johns in memory of his sister Courtney, who was killed in the crash of TWA Flight 800. She premiered in her own book (a rare situation, no doubt), and though it was short-lived, she started appearing monthly in Justice Society of America, which kept her in the public's eye and has helped make her very popular - which is why she also eventually appeared on the Justice League Unlimited cartoon: first in an episode set in Skartaris (as the bio on the card suggests), and later in a revival of the Seven Soldiers of Victory.
As mentioned, I planned to repaint Supergirl into Stargirl, and clearly Mattel's had the same idea, because Courtney is heavily based on that figure. The torso's been remolded to remove the S-shield, and she now has her cosmic convertor belt (which is both pegged and glued into place so firmly that you may not be able to tell it's a separate piece), but the arms and legs are identical. That's fine, though; Supergirl was a teenager, Stargirl is a teenager, so the small body suits her.
The head is new as well. Supergirl's head was too large for her body, but Stargirl's head is sized appropriately. She's got a fairly cute face (by JLU toy standards) and appropriately, she's looking up - at 3½" tall, she's puny next to everyone else! Really, the only thing missing is her braces, and I don't think a toy like this would have been able to show those.
Her mask has sculpted edges, not just painted on. Still, that's the area you need to watch out for when buying her: the mask can still get sloppy, and she's prone to walleye. The stars on her Yankee Poodle-inspired costume are all crisp. Her belt, gloves and the edges of her boots are all red, and she has white stripes on the outside of her shorts. The only bad thing about the paint is her skintone: it's very yellow, so she looks like she's ill; but still, you just have to chalk that up to the JLU style, not a conscious choice.
Most JLU figures move at the Big Five,
but Stargirl's hair keeps her head from turning at all, so she's just got hips and shoulders. She stands okay on her own, but since she's a girl, Mattel gave her a display stand to help keep her upright. Other than that, her only accessory is the same Cosmic Rod that Starman came with. You can jam it into her hand, but she's clearly not meant to hold it naturally.
Stargirl is a decent figure, but she's lacking anything to really make her special - perhaps if Mattel had remolded either her hand or the Cosmic Rod, so she could hold it properly, she'd be a standout, but as-is, she's merely a mediocre release, with nothing truly good, nor anything truly bad. If they ever get around to releasing a STRIPE to go with her (may we suggest a repainted Rocket Red?), she'll look nice next to him.