I dunno..
Here is one article about it..
And..
It's been rumoured that the twins had both gotten nose jobs right before they turned 18, as well as an eye lift to give them bigger and whiter eyes.
Here it looks like Ashley has did something to her lips as they're swollen, twice as large, and gross looking. Usually the upper lip should be 1.5 times smaller than the lower one, in her case it looks of equal or even larger size.
http://gossiprocks.com/uploader/files/1/ashleyolsenlips.jpg