Katie has decided to legally leave her last name unchanged. She will remain Katie Jacyna for legal purposes but has no issues with any gifts which denote the house hold as the "Walkers".
The second line is a type of parade historically associated with jazz funerals; the term "second line" is often thought originally to have referred to the secondary group of participants in such a parade, behind the band and the family.
Louisiana summers are very hot and humid. Plan to bring cool clothes and sandals - the reception will be cocktail attire so sleeveless and shorter dresses are no issue.
Airlines have different policies, please check the airline you booked with. Typically, you will need to call in (unless you have a frequent flyer number showing your credit) and rebook a flight to New Orleans.