I actually do picture her as being a good deal younger than her husband (but still much older than Tarannon's nephew Earnil). I picture her as a blonde too. I've seen a number of people draw Beruthiel as Middle Eastern or African looking, but I don't think it's likely that she looked like that. (The Far Haradrim were black, though I highly doubt that Beruthiel was from Far Harad.)
The appearance could make her easily 80 by the standards of Numenorian blood, which at the time had not thinned much. Her gaze as depicted by you could be read as analytical, or probing, as if to ask the viewer why he comes to request an audience. (If you had made all the cats mirror her glance, it would have been most sinister! ) . Beruthial wasn't a crazy cat lady, her pets were trained familiars, used to go on errands or spy on people, and punished if she was displeased with them. The white cat was her go-between and favorite. Tolkien did not say outright she was a witch or sorceress, but her loveless marriage to Falastur probably included royal displeasure at her interests. We might think it not too threatening, but the use (seeming or not) of magic to compel animals to action would have been unpopular with the people of Gondor, who would not have thought it harmless or humorous at all.
I think that training cats spying on people was the result of an unhappy personal life(as it is now would be concluded psychologist).All what she needed is a little bit of love,sex and two or three children.
Beruthiel has such a tantalizing portrait in Tolkien's brief characterization of her, you really want to know more about her and why she and Falastur didn't click. A king involved in empire-building, a magic-using queen, the Black Numenorians of Umbar, the martial-minded nephew, a queen written out of history, but remembered in folklore... A fanfic writer could have a lot of fun there.
Love it!! Not many people think of her, but I found the references to her and her cats very intriguing I was actually picturing her dark haired but aside from that this is really close to my image of her. Beautifully done!