From what you've written you need both need to sit down and discuss this out properly.
Why didn't she tell you before? Ask her...she will give you one of 2 responses. FIRST "I was confused" or TWO "I didn't want to hurt you". I don't believe anyone would be confused about his or her career. When one wants something, they will go for it no matter what, it's normal human instinct. Well think about it...had she told you earlier in the relationship that she was choosing to remain in her career, would you have stuck around? Quite clearly NO...so essentially she kept you around for as long as possible and was hoping that you would probably change your mind. Are you willing to do that?
She has clearly (after all this time) come clean and said she wants to remain in her career - the ball is in your court. You can either accept this and try to work out a relationship or you may have to end this and let her go. It's a scary thought, and yes it will hurt, but in the long run it'll benefit not her, but YOU. If you remain and further take this onto marriage, and remain miserable at the fact she's not at home with the family then what's the point? Similarly, if she does what you ask, and remains at home, she'll be miserable. Is that what you both want? I don't think so.
This is going to involve a serious discussion, and it's going to involve serious decision making. Sit down and discuss what you want out of the relationship and what she wants, and then try and come to some sort of agreement which benefits both of you. You have to respect that it's her decision and that's' what makes her happy. At the same time you have your own thoughts which she should also respect. If both of you can't seem to get it to work, don't be afraid to end it, you'll feel bad for some time but you'll live.
Good luck.