It's a risk, but she needs to be honest, and honest early on in the relationship in my opinion. If only for the fact that her partner may want children one day.

Also, it's not easy living with a guilty secret and it will always come out eventually. I recently lied to the girl I was with, for very good reasons. It ate away at me, and I had to admit the truth in the end. Of course she finished with me. Why wouldn't she? You have the right in a relationship that you are honest with each other. The minute that breaks down, it's game over.