[Opinions] Re: trying to name triplets here.
I personally wouldn't use more than one flower name in a set of siblings, triplets or not. Two sisters named after flowers is too cutesy, imo, but three is downright silly sounding. And even if it's two sisters with flower names plus one with a non-flower name, then that seems uneven and a bit off. So instead of one or the other, I suggest one flower name, and using non-flower (or even word) names for the other two girls.
How about....
Poppy, Viola, & Lila or Gwen
Poppy, Gwen, & Lila or Vivian
Poppy, Lillian, & Gwen
Poppy, Scarlett or Charlotte (instead of Violet) & Gwen