How does one go about re-entry to the United States with a shoplifting citation?

You should carefully consider whether it is wise to even travel outside the US at this time while you have a criminal case pending, especially so close to the deadline for filing your I-751 petition to remove the conditions on your temporary green card status. Instead, postpone this travel and wait for as long as it takes to resolve this matter. To do so, hire a criminal lawyer right away to represent you. If you do not have a prior criminal record, your lawyer should be able to get your case resolved with either an outright dismissal of the charges or a disorderly conduct violation without an admission on the record of plea to anything relating to shop lifting. As an LPR, you cannot afford a "hit" to any crime which may be grounds for deportation. While this appears to be a relatively minor crime. and for which a waiver is able to most LPR's I am afraid you may find that you do not qualify since you only just got a green card. Either way, to be sure you are making a decision you will not regret latter, you must hire an immigration attorney ASAP to work with your criminal lawyer in getting a safe disposition from the criminal court that will not negatively affect your US immigration status.

This should not be a problem and should not affect your green card renewal. Make sure you return in time to attend your court date.

You will want to discuss the situation with both your criminal defense attorney and an immigration attorney before you either agree to a plea. If you handle it well it will likely all work out for you.

You will be able to travel and return despite the charge. How it will affect your status depends on the outcome of case.

A simple petty offense arrest without conviction should not prevent you from re-entering the US with a valid LPR card. It should not prevent the removal of the conditions on your 2 year card if your marriage is bona fide. You should consult an immigration attorney.