I have read varying reports as to which were her favourite flowers, however I had not read about the cowslips before. Some say that she preferred lilies of the valley, a preference which served as the inspiration for the Faberge Lilies of the Valley egg. I have also read that she adored lilacs, both for their scent and their lovely colour, which was her favourite. She certainly loved fragrant flowers in any case, and her rooms must have always smelled wonderful.
The article
A Romanov Passion for Flowers on the main site says:
"Alexandra had a special love of lilacs, the color of the Mauve Room was created from a lilac branch the Empress gave to her decorator, Roman Meltzer, to duplicate as the hue for the walls and silk fabrics in her private boudoir. Lilacs come in many colors, some have intense fragrance and others are known more for their unique flower form or shade. The Imperial Greenhouses were able to supply lilacs to the palace almost all year. However the most beautiful, lush and fragrant lilacs came from the Imperial park itself, where huge lilac trees sunk under the weight of blossoms in early summer. The scent was overwhelming. In the far north, in Petersburg and Helsinki, lilacs possess an extra vigor and perfume because of the short growing season and long hours of sunlight during the days of the White Nights."As a северянин, Northerner, myself, I can vouch for lilacs smelling really good on these latitudes and being a cherished symbol of spring. Nevertheless they are only semi-wild in these parts. Our native fragrant flowering spring tree is the bird cherry (
prunus padus), which smells even stronger than the more subtle, aristocratic, lady-like lilac. In a Finnish source I saw the bird cherry quite fittingly described as "the cocotte of the spring woods", over-perfumed, "easy" and always attracting a lot of insects with its overpowering sweet smell! What might have attracted Alexandra to this even more fragrant, but immoral tree, is its native folksyness: In Scandinavia it's steeped in folk poetry and mythology, I wonder if that also is the case with the Черёмуха обыкнове́нная in Russia?
Bird cherry: 
