Yes they do make them. Invacare makes one called a hemi walker that is designed for people with mobility limitations in one hand. There are other companies too but this is the cheaper one. Unfortunately I can only find a listing for a set of two, which is around $75.

Here is the link:
http://www.phc-online.com/Hemi_Walker_p/inv-6252.htm

There is some great information on this page about them:
http://www.medicalwalkersonline.com/hemiwalker.php

Hope her shoulder heals soon.