Between Google translate and my own limited knowledge of the period I am almost certain that this is art of Romanian Crown Princess - shortly thereafter Queen - Marie of Edinburgh, wife of Crown Prince Ferdinand, and their first daughter Elisabeta in the uniform of the 4th Rosiori Regiment in 1904. One can in fact find a fairly decent amount of photographs of Queen Marie in the 4th Rosiori uniform on the web:

https://i.pinimg.com/736x/65/b9/19/65b91966ac9dc74e0afd83defea8328e--romania-uniform.jpg
https://i.pinimg.com/236x/47/01/09/4701092619ab96f3eec6fce4b42a3906--queen-victoria-colonel.jpg
https://i.pinimg.com/originals/d6/ea/d0/d6ead0b2c285d3c4c540527ccdc5d8e2.jpg

Elisavata has been clearly tagged on Pixiv by the artist as the subject of this piece. However her appearance may have been modeled on her sister Princess Marie (not to be confused with their mother): https://i.pinimg.com/736x/e3/25/29/e32529b6880e669a0d4982b34399ed1d.jpg

I'm inclined to think that this may have just been a mistaken caption on the part of the original photo because their respective ages appear about right for Elizsaveta and Carol, while Marie is very obviously younger in other photos from around that time.

The way mother and daughter are posed in this art is fairly reminiscent of an actual photo: https://i.pinimg.com/originals/a9/b1/f4/a9b1f4813f36d47dfb0f590c5befd11b.jpg