This one always comes up and it seems like nobody ever learns. I guess it's infrequent enough to where it's hard to search for the answers.
Just bring two nearly identical discs to the outing and hand her one or let her pick one. then just go have fun. don't make it more complicated than it needs to be. just laugh.
^^ this. i think the better question is, what discs should the more experienced player take with them when playing rounds with a beginner. personally, i take a putter, hand the other person a putter, stuff a spare putter into a bag just in case one gets lost, and we head to the first tee.