St. Bertha is listed as an intercessor for persons with mental illness as well. She was an abbess of a monastery in France, and a martyr.
Here is a Swedish site, translated by Google into English, on St. Bertha: http://translate.google.com/translate?js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&sl=auto&tl=en&u=http%3A%2F%2Fwww.katolsk.no%2Fbiografier%2Fhistorisk%2Fbavenay&act=url
The original: http://www.katolsk.no/biografier/historisk/bavenay
A letter written to her by Hincmar of Reims: http://epistolae.ccnmtl.columbia.edu/letter/1018.html