See this.

Her diary contains at least one heresy; that is enough for Pope Pius XII to place it on the Index:

On October 2, 1936, she states that the “Lord Jesus” appeared to her and said, “Now, I know that it is not for the graces or gifts that you love Me, but because My Will is dearer to you than life. That is why I am uniting Myself with you so intimately as with no other creature.” (Divine Mercy in My Soul, The Diary of Sr. Faustina, Stockbridge, MA: Marian Press, 1987, p. 288)

So, more intimately than with the Immaculate Conception?

“From today on, do not fear God’s judgment, for you will not be judged.” (ibid., p. 168)

Who, besides Our Blessed Mother, can escape God's judgment?

These denigrations of our Blessed Mother, coupled with the Divine Mercy Chaplet hijacking her Rosary, make me really suspicious about that devotion.

“And the host came out of the Tabernacle and came to rest in my hands and I, with joy, placed it back in the Tabernacle. This was repeated a second time, and I did the same thing. Despite this, it happened a third time.” (ibid., p. 23) … “Oh, no, here it is again. I have to go put this back now.”

Seriously, what kind of silly vision is this?

_______________________________________________________________________________
Also, Pope Pius XII banned Sr. Faustina's image "in the forms proposed by" her (which were?). See this.

See AAS 51 [1959], p. 271:

NOTIFICAZIONE

Si rende noto che la Suprema Sacra Congregazione dei Sant'Offizio, prese in esame le asserite visioni e rivelazioni di Suor Faustina Kowalska, dell'Istituto di Nostra Signora della Misericordia, defunta nel 1938 presso Cracovia, ha stabilito quanto segue:

1. doversi proibire la diffusione delle immagini e degli scritti che presentano la devozione della Divina Misericordia nelle forme proposte dalla medesima Suor Faustina;

2. essere demandato alla prudenza dei Vescovi il compito di rimuovere le predette immagini, che eventualmente fossero già esposte al culto.  Dal Palazzo del S. Offizio, 6 marzo 1959.

Ugo O'Flaherty, Notare

A notification of the Holy Office:

The Supreme Sacred Congregation of the Holy Office, having examined the alleged visions and revelations of Sister Faustina Kowalska of the Institute of Our Lady of Mercy, who died in 1933 near Cracow, has decreed as follows:

1. The distribution of pictures and writings which present the devotion to the Divine Mercy in the forms proposed by this Sister Faustina, should be forbidden;

2. It is left to the prudent discretion of the Bishops to remove such pictures which may have been already exposed for worship.

From the Holy Office, 6 March, 1959.

Ugo O'Flaherty, Notary

(source of translation)

_______________________________________________________________________________
And something that strikes me odd about the Chaplet of Divine Mercy is this prayer in it:

Eternal Father, I offer You the Body and Blood, Soul and Divinity of Your dearly beloved Son, Our Lord Jesus Christ, in atonement for our sins and those of the whole world.

Only Christ, through His priests, can properly offer Christ in atonement. It seems improper, to say the least, for laypeople to say this prayer. It would seem to make sense only if this were a prayer in the Mass.

I hope Sede Catholic joins this thread and makes some rebuttals, as he did on another thread here.

From today on, do not fear God’s judgment, for you will not be judged.” (ibid., p. 168)
Who, besides Our Blessed Mother, can escape God's judgment?

If you are in this friendship with Jesus (i.e. the state of sanctifying grace) then you should have nothing to fear from the judgement of God. when a soul reaches a certain intimacy with Jesus that is true, that soul should have nothing to fear from the judgement of God.

in the case of St Imelda for example.

Which was?

Also, Pope Pius XII banned Sr. Faustina's image "in the forms proposed by" her (which were?). See this.

See AAS 51 [1959], p. 271:"AAS 51:271" said:
NOTIFICAZIONE

Si rende noto che la Suprema Sacra Congregazione dei Sant'Offizio, prese in esame le asserite visioni e rivelazioni di Suor Faustina Kowalska, dell'Istituto di Nostra Signora della Misericordia, defunta nel 1938 presso Cracovia, ha stabilito quanto segue:

1. doversi proibire la diffusione delle immagini e degli scritti che presentano la devozione della Divina Misericordia nelle forme proposte dalla medesima Suor Faustina;

2. essere demandato alla prudenza dei Vescovi il compito di rimuovere le predette immagini, che eventualmente fossero già esposte al culto.  Dal Palazzo del S. Offizio, 6 marzo 1959.

Ugo O'Flaherty, Notare
"translation" said:
A notification of the Holy Office:

The Supreme Sacred Congregation of the Holy Office, having examined the alleged visions and revelations of Sister Faustina Kowalska of the Institute of Our Lady of Mercy, who died in 1933 near Cracow, has decreed as follows:

1. The distribution of pictures and writings which present the devotion to the Divine Mercy in the forms proposed by this Sister Faustina, should be forbidden;

2. It is left to the prudent discretion of the Bishops to remove such pictures which may have been already exposed for worship.

From the Holy Office, 6 March, 1959.

Ugo O'Flaherty, Notary

The Pope is certainly free to regulate the devotions which are practiced in the Church. As I recall everyone who was involved with these devotions obeyed Pope Pius XII.

Father Peter Scott wrote against Faustina in 2010

http://www.angelusonline.org/index.php?section=articles&subsection=show_article&article_id=2895

Father Peter Scott wrote against Faustina in 2010

He also wrote against the new rites of ordination and consecration.  So, I don't know whether the SSPX continues to hold any view on which he wrote.  In any event, I think much of what he writes is spot on.

Sure like the back issues of the SI SI NO NO are available
on the Angelus Site.