Dear Katie:

Concerning the Real Presence the Gospel of John chapter six gives us the teaching. Jesus said that "you must eat my flesh and drink my blood to have life". He was not speaking symbolically. We know this because the people he was talking to took it literally. They could not accept the teaching so they got up and left him. When they left Jesus did not call out to them and say "hey guys, I was only kidding. It's only symbolic." No. Rather, Jesus stuck to his teaching even to the point of risking the loss of the twelve. He looked to his beloved twelve apostles and said to them "will you leave me too?" Peter said, "No Lord, where would we go for you have the words of eternal life."

These passages were very significant and helped to convince me to convert to the Catholic Church because these passages prove from the Bible to Real Presence.

Show her the passages in John 6 and explain them to her. Then pray for her.

As for your sister receiving the Eucharist explain to her that she is not to receive Eucharist if she is not in the state of grace. If she has missed Mass or has committed any other serious sin then she must first go to confession before receiving the Eucharist. Even if she does not understand these rules of the Catholic Church is she needs to respect them.

You can explain to her how rude it is to receive the Eucharist in violation Catholic rules. It is rude to God and it is rude to the community. What if your sister had a rule in her house that guest must remove their shoes at the door so as to not track dirt onto her carpets. Now, what if guests rudely ignored that rule and didn't take their shoes off tracking dirt all over her carpets? Would she not think this person rude and a jerk? Now what if this person personally believes that such a rule is silly, or is not important? Will not your sister take offense of this?

Well when we come to a Catholic Church we come into the Catholic House or worship. We are in a Catholic House and thus the Catholic House rules apply. Unless we are jerks, we will follow the house rules even if we do not like the rules. After all it is not our house it is the Catholic House.

This is no different than if I came to your sister's house and rudely ignored her house rules.  If her house rules bother me that much, then I ought not come to her house.

Perhaps this will help her understand that she need to follow the house rules for the Catholic Church if she is to come to a Catholic House of worship.

One other thing, communion is not just the Real Presence, it is a sign of unity within the community. It is a sign that we believe all that the Catholic Church requires us to believe. If anyone doubts Catholic teaching, or denies Catholic teaching, then they are not to receive the Eucharist. To receive the Eucharist when one does not believe in the Real Presence is to tell a lie. It is a lie because to receive says, "I believe".

Thus, unless she wants to be a rude, lying jerk  she needs to refrain from receiving the Eucharist until such time she believes in the Real Presence and is properly disposed.

P.S. You may not want to use the "rude, lying jerk" part, but then again, maybe she needs that slap.

God Bless,
Bro. Ignatius Mary