Well, you're both half-right. Typically, sexing mbuna using egg spots is useless, as most females have them as well. However, when it comes to saulosi, MOST females actually don't have them, so it can be used with a little more accuracy than most species. But female saulosi have been known to get the occasional spot too.
But yes, I'm positive she's a female. I have 30 of her month-old fry in a growout, and the juveniles that I'm waiting to grow up (they're about 2" now) are her babies as well.