Well I agree with you on the gun. If she were really buying it for Bill I don't think she would have asked Finn about guns. She would have asked Bill what kind to buy. And the fact that he was shot with a 38 just days after she bought it sure makes is look like MM who did the murder. Again I wonder how such an intelligent woman could do some really dumb things in this crime. The only thing I can think of is that MAYBE she was thinking that the suitcases would never surface so everyone would think he just took off like she said, so no one would look into the fact that she bought a gun, etc.