They were not cited as such. But if you admit the fact that the revelation was authentic and that those words were communicated to her by the Father and the Son, then you would be directly contradicting the words of God Himself, which though not heretical, would be at least temerious.
In canonizing a saint, the Church in no way asserts that every teaching or belief of theirs is true (cf. St. Thomas on the Immaculate Conception) nor every revelation true or authentic. Even St. Theresa of Avila spoke about criteria for discerning between true divine locutions and suggestions of the imagination (criteria which she affirms she had to apply even in her own case). Consequently, there could be an admixture of divinely inspired thoughts and personal imagination.
Caminus, you need only read the words of your own St. Faustina.
This is just more special pleading. Let's face it, you just don't like the words so you are straining to disqualify it in any way you can, isn't that correct?
In this particular case, we have God the Father reminding her of what Jesus Christ said to her. In this particular case, we have an ancient, approved and authentic revelation to one of the greatest mystics of the Church. It is not an argument from authority, rather it is yet another piece of evidence in the long line of our doctrinal tradition which you reject based upon false premises viz. that there is a causal relation between these doctrines and liberalism.