MU193340

She will loose her green card. She can file for reentry permit that allows her to be out of States for 2 years max!
Without that permit (or if she stays abroad longer than 1 year ) she will lose her green card and won't be allowed back to the USA. Unless you file for spouse visa and go through the process again. 
 
She should be aware that green card means she needs to reside in the USA. If she wants to travel freely she needs to wait for citizenship. 
 

Re-entry permit, then renew if longer than 2 years (but have to return to US to renew). Can only renew ro max 5 years. Would probably be better to get dual citizenship first if possible. In either case, remember you and her still need to file tax returns with the IRS every year even while living abroad. Particularly important for her to do if she leaves as a green card holder rather than a citizen. Also if she leaves as a green card holder remember that time spent abroad in excess of 6 months interrupts her continuous residence requirement for naturalization.

1. Current time frame varies by different field offices, but generally prepare for 4-7 months wait from filing to interview. The civic test is extremely easy, she can study it on the weekend before her interview. It doesn't take that long to study 100 questions, unless she doesn't really feel comfortable with English. The civic test is only a part of the citizenship interview, she still needs to prepare supporting docs such as tax records.
2. Search on VJ and see timelines for people that are processed at your field office.
3. Overall cost is the N-400 filing fee, $725. 

I can share my experience.
- I submitted my application in early June 2017. Fingerprints several weeks later, interview in December, Oath ceremony in January 2018. Approx 6 months end to end.
- Mine was in Los Angeles, but the USCIS website has comparative processing times. The processing times page suggest that Milwaukee is 2 months longer than Los Angeles (https://egov.uscis.gov/cris/processingTimesDisplay.do).
- The citizenship test requires no more than 4-6 hours of study over the course of 2 weeks before the interview. All 100 possible questions are available online (and they give you a book with them at fingerprinting). There are no tricks here, its a very simple verbal Q&A, it's not a formal written test etc. It should not be a factor that decides your strategy.
- The (only) cost is $725 filing fee (https://www.uscis.gov/n-400)

Sweden does allow for dual citizenship ... and the US doesnt care how many you have.
 

Thank you. I have searched and have the exact same address that was provided on the envelope. The postal office returned the document and are equally as confused why it did not go thru. The return to address provided a different PO Box than is located anywhere on the internet and USCIS and I was wondering if anyone has recently had this issue with the I-865 to the Nebraska Service Center.