Ernst Ludwig wrote of her, after Henry's death:
"She is alone now but in spite of this she manages to do so much that she is sometimes completely worn out. Her only thought and concern is to find ways in which she can help people time and time again."
I don't believe she was hard-hearted, though she is rather overshadowed by Victoria's brilliance and Ella's saintliness. The fact that she cried when Ella converted is perhaps more indicative of her own religious beliefs and her concern for her father, rather than condemning Ella. Today, when religion is not so vital in the lives of many people, it may be difficult for us to understand the reactions of people of another era to whom adherence to a particular faith was imperative.
Regarding Marie, I think she has rather a selective memory and tends to be very bitter about many people. She originally wanted to marry then changed her mind, perhaps because she had 'cold feet' and she was dithering about when Ella told her to make up her mind. Isn't it possible that Irene's words were slightly twisted or exaggerated by Marie, later? Perhaps, seeing that Ella was ill at the time, Irene said something like, Ella is ill and doesn't need this added worry...it will kill her so make your mind up!!"
It's interesting, too, that Henry often gets 'a bad press' for his short temper etc. but Marie Mallet, meeting him at Kiel in 1896, said she and the other ladies-in-waiting thought him, "the nicest male royalty going" whereas Irene's ladies-in-waiting, she thought 'very dull and by no means easy to get on with.'