The point is: was Ekaterina Michailowna considered ugly in his time ? I have no documents on that, no memories, no letters ... and I do not read russian. Purhaps something could be find in the language of her husband (german but I do not read german...). I have a vague memory to have rode once that - as a young girl - in Russia she was considered charming and very cultured, with a sweet voice and sweet manners.
Many french travellers said that russian women of the nobilty were slight, beautiful in face, really cultured. So, beeng plain, E M was certainly different. She also married young (17een, I guess) and it seems her husband was deeply in love with her. I do not know if the niece that Nicolas wanted to marry Alexander was her... I thought (without a precise reason) it was Maria Michailovna (the one dead in Vienna of tuberculosis).
An other fact is that to-day, to be plain still means to be considered in some way "ugly" (as a man and as a woman).
Your friend
Mr Canard