I would have said the the clothing and the honors were wrong for Alix of Hesse as well.
This woman looks to be in deep mourning and wearing honors that look more British.
If he truly thought that Alix looked like that, I guess it is his opinion, but if this painting was done in 1889, who was she in deep mourning for?
She would have only been 17. That women looks far to old to be Alix at 17 and as yet unmarried and living at home.
In 1889 Alix, Princess of Wales would have been in deep mourning for her son Prince Albert Victor, but Alix of Hesse as a cousin would not have been in "deep"mourning.