T.S.
My son was potty-trained in a weekend just after he turned two HOWEVER, getting rid of diapers was something HE wanted to do. That said, I don't think 2 1/2 is too early, but just be prepared that it might not work the way you want it to (there are somethings you just can't control about another person :-P)
If at all possible, could your mom or someone come and stay with you and or take the little ones for a weekend so that you can to an intense weekend with your daughter? That could make a huge difference.
As for pul-ups, they aren't really different than diapers except that you can pull them off and on again easily. If you want her trained quickly, keep her in diapers and then switch to panties... However, since you've got two other little ones and don't want to drive EVERYONE crazy, pull ups are probably a great idea, but you'll need to let go of the get it done quickly thing.
Just keep her in pull ups and encourage her to use the potty. Go at regular times throughout the day (like 20 minutes after she eats or drinks anything) and give her a jelly bean each time she pees or poops in the potty. It'll happen more slowly, but it'll happen.
Good luck and enjoy your three little loves.