I don't want to mislead you, but I believe even though you are on different PNRs that they can probably, once you call them, tie your two PNRs together so you can be seated together, etc. That way, if you are an elite oneworld member, she can enjoy your benefits as well, and that includes preferred seating. I don't know if preferred seating is an explicitly stated benefit that guests can also enjoy, but each time I've called AA they have accomodated my preferences with anyone I have been travelling with. My son, who is CX silver (OW Ruby), traveled to SJU on AA for his spring break with 3 other non-oneworld members, and he managed to get them all seated near him on an A300 near the front of Y. So they do try.