You have to seriously consider going to the police on your own. It's going to be a hard decision to make, and you have to think about how it would affect your friend and how it would affect your relationship with her. But if she's seriously suffering, and her daughter is as well, you have to at least consider doing your best to stop this.
About your last sentence: "They say marriages are made in heaven but the more I look into it the more I get convinced that Marriage is a one way to Hell!" You might want to consider the fact that it depends who you end up with - if you end up with someone caring and loving who constantly challenges you to be better, and supports you when you're down - then your marriage was probably made in heaven. If you strike out and end up with someone like this - then you're probably right. I wish you the best of luck in making that decision, and hope that your friend's situation only improves.