I don’t think naming this daughter [name_f]Violet[/name_f] will ever make [name_f]Libby[/name_f] seem like an afterthought. That you carried her, chose a name specially for her, talk of her often and continue to keep her memory alive shows the important place she has in your family. The similarities or differences between her name and your other daughter’s names don’t come into it. [name_m]Just[/name_m] like if you choose a name that shares some sounds with [name_f]Libby[/name_f], it wouldn’t be leaving [name_f]Iris[/name_f] out.
I think the intention or reason for choosing a name matters more than the actual similarities or differences themselves, so unless you told me otherwise, I would assume you chose all your daughters names because you loved the names or they held significant meaning for you. The flower connection between [name_f]Iris[/name_f] and [name_f]Violet[/name_f] would sound like a coincidence, nothing more. So please don’t let that thought hold you back if you want to use [name_f]Violet[/name_f] as a first name.
Now onto the names themselves. [name_f]Susannah[/name_f], [name_f]Violet[/name_f] and [name_f]Clara[/name_f] all work well in your sibling set. The styles are very compatible. I only hesitate with [name_f]Violet[/name_f] because of the strong vowel sound it shares the with [name_f]Iris[/name_f], especially since it’s the first syllable in both that is stressed. I like all the mix and match combinations you can make with these three names. [name_f]Violet[/name_f] [name_f]Clara[/name_f] is just a bit tricky to pronounce with the two ‘L’ sounds.
Here are some other suggestions you might like in the traditional and vintage styles: [name_f]Mabel[/name_f], [name_f]Felicity[/name_f], [name_f]Beatrice[/name_f], [name_f]Helena[/name_f], [name_u]June[/name_u], [name_f]Edith[/name_f], [name_f]Phoebe[/name_f], [name_f]Ruth[/name_f], [name_f]Norah[/name_f], [name_f]Sylvia[/name_f], [name_f]Esther[/name_f], [name_u]Camille[/name_u], [name_f]Ada[/name_f], [name_f]Miriam[/name_f], [name_f]Naomi[/name_f], [name_f]Faye[/name_f], [name_f]Jemima[/name_f], [name_f]Esme[/name_f], [name_f]Vera[/name_f], [name_f]Tessa[/name_f], [name_f]Martha[/name_f]
All the best with your search and decision!