If a client wants a Twitter Feed on their website they can create a widget in their Twitter account and use the Embed Code app to display on the page.  However, if they didn't stipilate the width of the window when creating the widget then here is the code you can add to adjust the width to 100% of the region the app is placed in.

At the end of the code provided from Twitter add:

<style>

          .twitter-timeline{width: 100% !important;}

</style>