I supposedly have red stars (that's what they told me) and they all have large combs and wattles. I'd be looking at the hackle feathers. If they're pointy you've got a roo, rounded is a hen. It takes a while for spurs to grow in, and even hens sometimes have tiny ones. You're hen cannot "turn into" a rooster, by the way. For comparison, just cause a man might like dressing in ladies clothes, he won't suddenly become a she. Same with your hen. She might just ACT like a roo.
I thought red stars had white roos? Or is that just "red-sex link" birds?