Actually, only Catholics in a state of grace should receive the Eucharist, but that’s another thread (sadly).
I would also tell your friend that the Eucharist, to a Catholic, means the Real Presence–Body and Blood, Soul and Divinity of Christ, not just a memorial, not just a symbol- and that reception would mean that he or she would not only have to totally believe that teaching, but all other Catholic teachings as well, and thus of course that would mean he or she would need to start the RCIA process to become Catholic if he or she truly does believe in the Real Presence, since certainly then he or she would also then be bound by St. Paul’s exhortation that one not only receive ‘worthily’ but be bound to the authority and the rules of the Catholic Church.
IOW, if they believe what we believe about the Eucharist, then for their own sake they need to become Catholic in order to receive because they obviously recognize the truth of the Catholic faith.
If they don’t believe, then reason alone should preclude them from ‘taking’ something which they themselves do not believe in; certainly good manners would likewise dictate that if Catholics say the Eucharist is one thing, and these people are in a Catholic Church at a Catholic service, then to blithely bypass the Catholics and ‘take’ because, hey, in my church it’s something else, so I don’t care what **you people ** believe" would be astonishingly ignorant and rude. . .
Gracious, I wonder how they would feel if a nonChristian came up and stomped and tore their Bibles because, “Hey, in my belief system this is a nasty, bigoted piece of fiction that we trash–so while I’m at your church I’ll treat this book exactly the way I would outside of your church.” I don’t think they would be very happy. . .