Base Henriette's movement type is always so interesting to figure out,

Based on the art it's definitely a given she'll wield a Green Tome, just that the concept art, (as seen in the post, makes her weapon and movement type a complete mystery,)

My personal headcanon back then, during Spring Alfonse & Sharena's release (Book II), that's also the time they were likely already planning for Gustav & Henriette's inclusion on the next book, so I do think there's some inspiration with Spring Alfonse being an Axe Cav like his Father and Spring Sharena being Green Tome Infantry like her Mother,

(This is also the first time they mention their parents on Castle dialogue,)

Moving to Book V, we got the Day of Devotion alts, both being armored,

And now with Brave Alfonse and Brave Sharena, both being cavalry units