I'm going to say that Rosie and the Wedding Day Rescue, the first book in the series, is definitely the weaker of the two. I picked up my copy for free from Amazon during a promotional period (I keep up with Kindle freebies over at /r/FreeEBOOKS), but I didn't get around to reading it until now. It's short and it's cute, though it's not exactly the most fascinating or logical thing I've ever read.
It's really exactly what you'd expect it to be. Three cute little girls (making up your typical white/blonde, white/brunette, and ambiguously brown/brunette trio) are invited to be flower girls at a wedding, and they get to pick out their clothes, deal with insecurity, and solve all the bride's problems along the way. Because of the low page count, though, there isn't much time devoted to any of these issues, and I'd say the "helping the bride" bits suffered the worst for that; but then, I always find these kinds "the kids save the day" plots kind of ridiculous--but I'm sure a kid within the age of the target audience will get a kick out it no matter what I think.
Iris' new friend, Hana, is a mixed-ethnicity girl of Chinese, Japanese, and Hawaiian descent, and her Tutu--her grandmother--introduces the reader to some Hawaiian mythology in the form of the Menehune. It really helped to make the Hawaiian theme seem less like empty trappings thrown on for the sake of exotic flavor and more like actual cultural diversity, and I loved it. Had I read this as a kindergartner, I don't doubt that I would've adored it.
At the moment, the Flower Girl World website has no information about any upcoming books in the series, but if any more do come out, I definitely hope Woolley keeps going in the direction she took with Aloha Wedding Adventure. As for me, if I spot any more FGW books on Netgalley in the future, I'm definitely going to give them a chance. I'd love to see this series go further with the cultural exploration and get into different wedding traditions around the world.
Iris and the Aloha Wedding Adventure was downloaded free via Netgalley in exchange for an honest review.