The reasons Christie Vilsack will run and win in the new 2nd
1) She wants it. She's made that pretty clear. And the 2nd is her only viable option to Congress. Running in the 1st would be worse, running in the 3rd would be mutually assured destruction for her and Boswell. The only other real option is the 4th and while she would be a hero for taking on King, it would be very tough to win and even tougher to hold. Which district would you want to represent if you were her?
2) Money won't be a problem. She is married to the sitting Ag Secretary and is BFFs with the Clintons. This is regardless of whether the DCCC supports Loebsack, which is an open question (it is not the same analysis as supporting Boswell because Loebsack is newer and the Dem will win the general regardless).
3) She has a base in the 2nd. Her husband ran up big margins in far SE Iowa during his Gubernatorial campaigns. She still has a lot of connections down there. Not only that, but Loebsack has been remarkably weak in those counties (Henry, Jefferson, Des Moines, Lee, Wapello, etc) and there are still a lot of Democrats down there. Loebsack has no base. Johnson County would be the closest thing to it and Iowa City would obviously be the big prize in a primary, but she could compete there.