She was questioning the morality of the OP’s feelings.
NFP, by it’s very nature, rids us of the so-called contraceptive mentality. If we are to uphold the sacredness and importance of sex in our marriages, than it really helps us to recognize the sacrifice involved. It makes us deliberately think about it. Are our motivations worth it? It purifies our intentions. But it does this in the long run and it often takes us on unexpected turns.
The Myth of the Contraceptive Mentality
The fear that comes with taking a first step in obedience to our faith is normal. What she needs is the encouragement to keep going. Practicing NFP and getting that support, will help with those anxieties on their own. Condemning her for her emotions is like condemning someone whose just learning to play the piano for being nervous and not playing like a master. Let’s appreciate her step and be patient. Let’s not pat ourselves on the back and guilt people for not being “as good as we are” and then cover our pride up with the false humility of generic conversation about how deeply sinful we are.
Its like condemning a person who hasn’t been to Mass in 10 years for coming to Mass in jeans. Both of you are failing to see God’s grace here and focusing instead on the negative.