It is important to understand some of the dynamics around this problem.  First and foremost, your mother should be seen by a doctor to rule out any possible medical causes. Incontinence can be caused by conditions that can be treated, such as urinary tract infections, medications, or dietary issues.  If your mother has dementia or any other cognitive impairment, she may not remember the process of visiting the bathroom nor may she remember how to communicate this need.  Determining the cause is the first step, which is the reason a visit to a healthcare professional is essential.   
 
You mentioned she refuses to wear Depends, which is a common dignity issues for many individuals.  If you want your mother to accept wearing an undergarment you need to make sure to approach the subject with respect and kindness.  For most people, using the bathroom is a part of the daily routine that does not require much thought; however, there is much mind/body coordination that does take place.  Your mother may feel that she has to go but may get confused about finding and using the restroom, disrobing, and attending to her body.  I suggest utilizing undergarment products that function more like underwear, such as a pull up style.  You can visit web sites that offer incontinency products, as there are more innovative products on the market to protect her sense of self and enable her to retain her dignity.  You can begin by viewing the products on the the e-store of the Alzheimer’s Foundation of America at http://www.alzfdn.org/AFAStore/estore.html.