This could be a dumb question and I think this was answered before, but can my fiancee travel in the U.S. once she arrives here?? We are planning to visit friends and family up in the mainland. Thanks!

Absolutely, I'm a K-1 and had no problem at all travelling around here. They didn't even look at my visa on domestic flights. Once she's in - she's in, at least for 90 days until you guys get married. Then you'll have to file for AOS and she can't leave the country without advance parole until it's done.
My husband jokes "First they wouldn't let you in, now they wouldn't let you out"

I suppose being from another country, it may seem unusual or not normal. However, in the United States, you can visit all of them without worry. I don't know if you'd have any problems with Alaska/Hawaii (being separated physically) but I doubt that matters. I DO see an issue with Puerto Rico, and trying to return after a visit.

Well, it is the "United States" and with that there is no required visa to visit each state. You will have to cross a border, but there are no police wanting to see your Visa.

Of course he/she can visit any state possible within the United States of America. That includes North Dakota too.

Did you plan to lock her in the basement?