I too suffer from chronic depression. The cause of mine is endogenous, though – I am a survivor of a bleeding brain aneurysm, and i am unresponsive to all antidepressants available on the market, so I’ll be this way the rest of my life. I assume your mom’s depression is exogenous (of external, or psychological origins?) Whatever: read my blog [link below] about my aneurysm experience and my depression – how I feel my brain has adapted to a “different” level of feeling, eventually, so it’s not as bad as it sounds. I hardly notice my own depressions.
If your mom’s dysthymia IS long-lasting, like mine, I predict her brain, too, will adapt to its new way of feeling.
MY BLOG : http://nothingyoucansee.wordpress.com/