I'm with chantal on this one. They should have done a complete exam before going through with the operation. And even if they, for whatever reason, could not detect the baby at 8 weeks, they should have at least seen a gestational sac in the uterus by that time. And as Chantal mentioned, if she is 3 months along, I wouldn't trust the accuracy that she is having a girl. Generally women don't find out what they are having until 17 weeks or later. The boy/girl parts don't even differentiatie until after 14 weeks. Either way, some more info would be helpful as to the timeframe of when she had the operation and when she found out she was pregnant again. However, if everything is as you mentioned, then congrats.
How long after the ectopic did she find out she was pregnant with this one? Didn't she have an u/s before having that operation to see if there was a baby in the uterus? You can detect a baby in the womb by 8 weeks for sure! I have never really heard of your particular situation....maybe someone else has some insight on this. they could tell she is having a girl at just 12 weeks? I'm not sure how accurate that is at this stage. but if she is pregnant again and everything looks good, then congrats! =)