We can’t condemn anything approved by the church. Even more , St Faustina made many miracles which shows the work of God in her and all she is saying is how much God is Merciful so there is nothing wrong in that and the prayers are so beautiful. Furthermore , Jesus said similar things to St Gertrude the Great about His union with her.
Our Lord’s words to a devout person who was praying for Gertrude when she was still alive at that time as they are written in the Revelations of St Gertrude’s book:
After Our Lord had spoken this to this soul, He showed her a precious stone on His heart, in the form of a triangle, made of trefoils, the beauty and brilliancy of which cannot be described; and He said to her. ** “I always wear this jewel as a pledge of the affection which I have for My spouse. I have made it in this form, that all the celestial court may know by the brightness of the first leaf that there is no creature on earth so dear to Me as Gertrude, because there is no one at this present time among mankind who is united to Me so closely as she is, either by purity of intention or by uprightness of will. They will see by the second leaf that there is no soul still bound by the chains if flesh and blood whom I am so disposed to enrich by My graces and favors. And they will observe in the splendor of the third leaf that there is no one who refers to My glory lone the gifts received from Me with such sincerity and fidelity as Gertrude, who far from wishing to claim the least thing for herself, desires most ardently that nothing shall be ever attributed to her”.**
Pope John Paul II said: “The message she brought is the appropriate and incisive answer that God wanted to offer to the questions and expectations of human beings in our time, marked by terrible tragedies. Jesus said to Sr Faustina one day: ‘Humanity will never find peace until it turns with trust to the Divine Mercy.’”
And the enemies of God said similar stuff about the Holy Rosary when Saint Dominic and others were preaching about it. See it here :
catholictradition.org/Classics/secret-rosary9.htm
catholictradition.org/Classics/secret-rosary10.htm
So don’t be deceived and believe false accusations made by the devil himself to destroy such a great devotion!
God Bless!