Buttons?

She specifically said they don't wear buttons on coats. The only buttons we see are on their shirts. So, while factually incorrect, it makes sense within the movie universe's logic i.e. the "no buttons" rule only applies to coats and vests.

"I mean, really, how many times will you look under Jabba's manboobs?"

It's also true that the Ordnung and its exact rules vary from community to community.Some Amish communities allow bicycles, for instances, or tractors with steel wheels that can go on land but not the road.

The Amish, in general, use buttons on shirts and pants, but not coats. See here:
http://listverse.com/2012/10/29/10-things-you-probably-dont-know-about -the-amish/

I didn't see them on any coats in the film, did you?