I rather like the girl being human. Gives a nice start-crossed lover feel. But you could try not using Mucha. He skews HEAVILY to flowers and women and is probably fighting your prompt. Just use art Nouveau, lithography and his palette to get the look and avoid humans.
Soft Pastels and Muted Earth Tones:
Ivory, Cream, Pale Beige – backgrounds, skin, and drapery
Alphonse Mucha: A romantic embrace of a “metal man” & a “metal woman”, both are vintage early 20th century human-like robots, made of riveted steel and brass. Both robots wear flowing capes with star motifs, in a floral archway. Use Mucha’s Art Nouveau style, ornate patterns, soft colors, semi-realistic, ...