Pink brought Linda Perry to life, without her there would be no mature Xtina and others
Pink is the most influential pop/rock artist of 2000s
Stupid Girls set the trend for pop culture mocking videos by female artists (La La Land by Lovato comes to mind first)
Her influence in Australia is huge. All talent show winners just copy her songs, cause it guarantees them a hit
She may not be a hugely noticed trendsetter, but she basically brought the whole "confessional" album to the forefront with Missundaztood. Suddenly, Xtina releases Stripped a year later, Avril attempts to be deeper with Under My Skin, Kelly Clarkson releases My December. You can say that these girls weren't necessarily looking to her completely, but you can't deny that her success with such a personal album helped open the gate for the rest of them.
I'm not sure if she's a trendsetter in the literal sense of the word but she's most certainly not a trend follower. I think Pink has always found her way to do her own thing no matter what cards she's dealt. I vote trendsetter.
She's more of a trendsetter than a follower, I guess. I feel like she's kind of off in her own world of amazingness, without the other girls "following" her for the most part.