It shouldn't affect anything, but you might get email instead of her. As long as it's used legally, I don't think Apple cares who registers the software, especially if it's a family member.
A person could use iWork to create webpages to solicit illegal acts, defraud a n entity or to publish State secretes. You could also use an unlicensed version of a software program, and some refer to this as being illegal. Perhaps doing something prohibited in the ULA, that would be illegal. (Does anybody ever really read every ULA all the way though?) Or, if you use the computer while entering the U.S. without permission, even if you have a licensed version, everything you do is illegal.
Odd, we don't refer to carjackers as illegal drivers, or thieves as illegal citizens. Well the term is stuck now.
I was commenting on the current immigration an labor politics. There is only one crime that makes a person illegal in the U.S., and that is entering with out papers. A murder may commit a crime, but they are not referred to as an illegal person. Some of the rhetoric has even go as so far as to state all work that an undocumented laborer did was illegal. I don't think that there has been enough thought to the language used by the media, as well as the fact that nobody seems to be noting the illegal employers, who employed undocumented workers.