I live partially in Maine, so Ill answer this. She is generally seen by many as a part of the Portland coast, your elitist Democrat, if I may use the phrase. She is also a boring moderate who doesnt really have a flare to them as Sweet did. Cote had a business background going for him, but Mills is much closer to a career politician. Her opponent, Moody, is charismatic, young, and a business owner. While the Republicans are having a hard time in the state after Lepage, he can still pull a victory. But, after everything Ive seen, the state will probably vote Mills by a weak margin.
Mills is actually from Farmington which is inland in the second district. She destroyed Cote in inland and northern areas which tend to be less elitist/wealthy. Cote actually won in Cumberland County (Portland and surrounding wealthy areas). She's more moderate than I am but she's tough, experienced, knows her crap, and can get things done (as Attorney General, she secured $35 million in a tobacco industry settlement and wants to use that to fund Medicaid expansion).
Also, Moody is going to be 59 in the fall. Younger than Mills but not what I'd consider a young buck or anything.