How can I find interesting, challenging activities for my very alert and intelligent mother?

We live in a somewhat rural area, with few or no activities that would stimulate my loving, engaged and alert 90 year old mother. She is VERY active on her computer, has a Facebook account, and is very attuned to current events. She lives close by in her own home, and is beginning to have a number of physical challenges that are all being addressed by the doctors that I take her to regularly. These challenges include COPD, difficulty in walking and colitis. We both moved to this area a few years ago, and my mother, who has never been one to have girlfriends or other acquaintances, enjoys her own company. Her favorite activity was gardening when she was younger and able to do so. She has a lovely yard in this house, but can't get around easily to do the kind of yard work she once enjoyed. Now that we are in this area, I have tried hard to find things for her to do. One of the drawbacks is that she smokes cigarettes, and does not like to be around other people because she feels that she will be judged. In addition, her addiction to cigarettes makes her crave one every hour or so, at the very least. Of course, there are very few places she can go that allow smoking! She has tried just about everything to quit smoking, including the patch, hypnosis, quit-smoking classes, etc., etc. and I have supported her in every way that I can think of. However, at this stage in her life, I don't think it will happen. She is not interested in church services or activities, but I KNOW that she would like to be around other people occasionally. For example, whenever we go to the doctor, she strikes up a conversation with any stranger in the waiting room. She will strike up conversations with others while sitting and waiting for me to park the car at the supermarket or any of the few places we go. Since I'm a retiree, I visit with her daily for at least 3 hours and my husband visits and helps around the yard as well, but we are her only 2 friends. My father died 20 years ago, and I am her sole caregiver. No other family members live in this area. I tried to find a senior center, but although I will drive my mother anywhere she wants to go, and at any time, the only center I could find is about 30 minutes away, and she doesn't want to ride that far!! I take her out for lunch or dinner whenever I can persuade her to go, but the trips to the doctor and a few lunches or dinners are her only activities. I'm at a loss as to my next steps, and I hope that someone on this forum can help with suggestions. I think this forum is EXCELLENT, and I am CERTAIN that it has been a great help to many who are struggling with issues much greater than our own. Any information you can provide will be much appreciated!