My sister is about to return from New Zealand to the USA. She mistakenly took her expired EAD card (document related to work permit) instead of the renewed one. Is there any possible way I can hand over the card to her before she passes through immigration? EAD is mandatory for her to re-enter the USA.
If the document is required for her to legally enter the US, then she will be denied boarding at the place of check-in and she won't make it to the US in the first place. If she doesn't need the document, you can give it to her once she is through.
If by some magic she manages to actually get on the plane, you would have to contact the airline. You cannot get into the pre-immigration area yourself, but the airline can. They may be willing to assist specifically since they can get fined heavily when presenting passengers that do not have proper documentation to enter the US.