It's been a long time since she's let me do anything with her hair. Occasionally, I've been able to sneak a barrette in if she's properly distracted, but pigtails have been unheard of. I finally figured out if I bribe her with a lollipop, she'll sit still long enough for me to put her hair up (I bought a bag of Dum-Dums as reward for potty training since there's less risk I'd eat the bag myself than if I would've bought M&Ms). By threatening to take the candy away once her hair's done, I've finally gotten her to leave it alone. It only takes a few threats before she's completely forgotten about the pigtails and moved on to something else.
Her hair's gotten so much longer since I first put it up in pigtails!