Ok 4 times is not too many, so there is plenty of time for practice!

You say she comes on her own, so its either just a problem with technique, or possibly with some emotional or psychological problem she has with orgasming with a lover. But more likely is the question of technique.

So top of the list now is for you to ask her to show you exactly what to do. She has to put her fingers onto yours and move your fingers about in exactly the way she likes it, the exact same way she uses when she masturbates.

Sometimes the experience you gain from being with other women doesn't actually help, because the clitoris is quite a versatile little organ, and can be stroked in many ways. Usually a woman masturbates more or less the same way each time - but that way is different for each woman! So now you are with her, you have to re-learn your technique. Some like having their clitoral foreskin moistened and then pulled back gently and having their exposed clitoral glans stroked, but other women hate this!

So since you've only tried 4 times, there's a lot more room and time for practice, but the main thing now is to get her to show you how.

Another factor is that she has only been having sex for a year, so it takes time for women to become comfortable with all aspects of sex play with a lover.