I offer my sincerest condolences.
I'm not a Christian, but please consider what I have to say.
When something bad happens, we have a natural tendency to want to know why. We want to know who's responsible so that we may blame or credit them. Did somebody screw up? Was it done on purpose? What reason is there? What kind of plan involves the death of this particular individual? We ask these questions because, as hard as it is to accept death as being a part of some sort of plan caused by someone, the idea someone can die for no reason at all outside natural circumstances can be the hardest to accept. If a person dies not for a greater cause, nor for someone else, it feels like their death is in vain.
Of course, as a Christian, you will likely conclude that God wants her in heaven. That she died according to his will. This still begs the question, why? Why would he leave children motherless?
If you conclude Laura's death to be a natural tragedy, you will feel cheated. And if you conclude Laura's death was according to a greater plan, you will be left confused. Either way, you won't know the answer until you're dead - and maybe not even then. So don't dwell too much on seeking an answer. She has passed away, and whether you have an answer or not, you won't be able to change what has already happened.
Cry for her. Miss her. Mourn for her. But do what you can to find happiness. This will be most difficult for her children and her husband, so your goal should be to help them first and foremost (as well as anyone else who may be more heartbroken than you). Help them appreciate and embrace the things Laura did for them. Help them learn how to be happy without Laura, so in the future they may smile when they think of her rather than break down.
Why did Laura have to die? Was there a purpose? What could that purpose be? Even if you conclude it to be a part of God's plan, you'll still ask why. So instead of dwelling on this unknowable issue, you need to focus on what you can know. Look at all the good Laura has introduced in the world, and continue the work she has started. Whenever you think of Laura, think of all the ways she's helped you and use that energy to help others - especially if it's something you wouldn't normally have considered doing.
All we can do is try to better the lives of other people and ourselves. And if we can appreciate the good of those who have passed away before us, then we can learn how to appreciate our own life even more as well as the lives of those around us. You'll find this to be true regardless of your religious affiliation, whether you're theist or atheist.
Choose to remember the positive things that she brought to your life and to the lives of her family and friends. Focus on being there for her stepdaughter and new little one. Her kids and family need all the support they can get right now. 
