Information on Napolitano and Immigration from the Daily Kos:
Signed Western Governor's Association's Climate Change Initiative
Criticized DHS as a badly organized agency early on.
Anti-Iraq WAR "The Iraq is probably most important issue to Arizonans today" 
Napolitano beat the grandson of Barry Goldwater. He was a Minuteman and he ran on anti-immigrant slogans.
Opposed Real ID "It's an unfunded mandate." "Are we going to make every DMV clerk an expert on immigration?"
Said that Passport requirements for the border would cost border businesses. "We don't have the necessary infrastructure at our ports to implement this yet. We can do it, but we need the technology and manpower installed first."
She has championed new methods to fight border crime while preserving civil liberty (always a fine line in border states) and respecting immigrants rights.
Napolitano championed legislation to fight Identification Fraud and put into place the former commissioner of the ATF to oversee training and tactics to enforce stricter ID Verifying.
Try buying beer in Arizona, most local corner stores will look your ID over and compare it in their book. Sorry teens.
Stolen cars heading to Mexico is a common event in a border state and Napolitano took it head on with a 20th century technique. She implemented a program to ID stolen vehicle license plates with traffic cameras. This allowed police to track stolen vehicles in almost real time and block their passage into Mexico where they would assuredly escape conviction. This move saved Arizona from beating New Jersey as the Car Theft capitol.
Napolitano was the first politician to quote the Governor of Sonora, Mexico when describing the border wall,
"Show me a 25-foot tall fence and I will show you a 25-foot ladder."
Gov. Napolitano National Press Club 2006
Here's the video of a great and in depth interview at the National Press Club
She decried the Minutemen Civil Defense Corps as "vigilantes" .
She often bristols when asked about the suspension of in-state tuition to the children of illegal immigrants. She has often defended the rights of children of the undocumented vigorously saying anti-immigrant politicos "-use bumper-sticker quotes that get little done to solve the problem."
She may not be perfect on the issue of immigration, as rarely a politician in a red state can be. But she is surprisingly close and often illustrates a nuance in understanding few politicians even in Texas have.
Her legislature enforced strict regulations on the hiring of illegal aliens. They sought to penalize those who hired illegal immigrants with stiff fines.
Personally I see nothing wrong with this idea, however it must be met at the same time with a guest worker program and comprehensive reform. But it was specifically the severity of the punishment that got her criticism from immigrant groups- not the law itself. Those to the left of me were far more outraged in Arizona.
Even still Napolitano has the highest Governor approval ratings in the country, and she got them in a red state. Yes even more than that Palin person (who's that?) whose numbers have tanked recently anyway.
National Immigration Forum Reacts to Apparent Selection of Governor Napolitano as Secretary of DHS November 20, 2008