My 60ish mother has been using a laptop with Ubuntu on it for nearly two years now completely trouble free. She runs the updates periodically when prompted on her own. Otherwise, the only support I have to give her is once every 6 months I tell her when it is safe to upgrade to the latest version. In contrast, she last ran Win XP for years. Though, inevitably her XP system slowed to a crawl or was infected by something or other at least twice a year. Worse yet, her XP was a money pit in virus scanners, malware programs, and other subscription bases services required to keep it running.
To address the rest of your concerns:
Confusing distros : One word: Ubuntu
Poor documentation : Again, Ubuntu has fantastic documentation and its all free
Software, Software, Software: Not really a problem. My mom uses OpenOffice, Evolution, and loves the Software Channel built right into ubuntu. She browses this herself, finds games and stuff, and best of all, I don't have to worry about some foreign shareware scamper ponwing her computer. Would you dare allow your mother to download software for Windows off the internet on her own? Oh, and for your sewing machine software, can pretty much guarantee you that it is usb or serial interface completely supported in Wine.
Little support: Ubuntu forums rock. Great people, great support. I know that to be true as I try to "give back' by answering at least a few requests for help a month.
Ways of doing things that are confusing to a Windows user: My computer illiterate mother had no trouble at all switching to Gnome. In fact, she finds the interface less cluttered and easier to navigate than Windows. Yes, there was a short learning curve, but she caught up quickly
In the end, my 60'ish very typical mother who is by no means a computer geek is completely in love with Ubuntu. In fact, she swears she will never own another MS product again. Hope this is food for thought. Maybe it is time to try again.