I realize this topic might upset some people, so I would ask for your patience in reading what I have to say.
In her memoirs, Marie Pavlovna the Younger relates a story about Ella that I have always found extremely disturbing. She writes that after the murder of Rasputin:
"My aunt clearly realized all the complications that were arising in connection with the death of Rasputin, but she was so happy at his disappearance that she could not condemn the murderers. To her, Rasputin had been a living and active personification of evil; and she felt that Providence had chosen Dmitri and Felix to perform judgment upon him. (...)
"Not knowing any of the details [of the crime] my aunt sent Dmitri an enthusiastic and probably incautious wire which was brought to the attention of the Empress. As a result, she had been accused of complicity.
"And now, in spite of her devotion to her sister and of all her Christian feelings, my aunt's patience was at an end."
IMO, if this story is true (and I stress the "if"), it does not reflect at all well on Ella's character, much less the depth of her "Christian feelings." I know that others have argued back and forth at length about certain character flaws Ella might have evinced before the death of her husband: for example, her "selfishness" and "coldness" to Marie Pavlovna when Marie was a child. But the incident I speak of happened long after the assassination of Grand Duke Sergei and Ella's spiritual epiphany - she was already a nun and the head of her own order, not to mention a future saint of the Orthodox Church. Yet here we find her sending her congratulations to a murderer on the occasion of his crime! Moreover, she does so in the full knowledge that her action, should it become known to her sister Alexandra, would deeply wound her.
It seems to me Ella behaved irresponsibly and cruelly in this instance - certainly not in a manner that can be described as worthy of a future saint.
But do we know if this story is even true? As far as I have been able to discover, Marie Pavlovna is the only source for it. Of course, Marie had her own reasons for portraying her aunt in an unattractive light. On the other hand, Rasputin's murder happened after Ella and Marie had reconciled; it was committed by Marie's brother and supported by a large number of the imperial family; moreover, in the passage I quoted above, Marie is being critical of Alexandra, not of Ella and her "Christian feelings."