Here’s a basic way… and it’s the way I usually do blue eyes but it will work with any eye color. It involves only one color that’s been either lightened or darkened.
Take a brush full of your main color and mix it with white. You want a very pale shade of your main color… and you want it thin, thinner than ink consistency. With that you are gonna make a crescent moon shape on the bottom of her iris. That’s the highlight.
Then you take a brush full of your main color and mix it with a tinch of black. You want a slightly darker shade of your main. Make sure you thin that too. Now use that to darken the top of her iris just below her eyelid. That’s the shading. You can also use that darker shade to outline the entire iris.
Now take your thinned main color and make a few tiny tiny bicycle spokes over both your highlighted crescent moon shape and the darker shade of her iris. That just adds a bit of detail and gives a bit more depth.