Most people have completely missed the point in this thread. In short, the answer to the OPs question is NO.
There is no strain of cannabis PERIOD that is legal to grow, unless you live in a help friendly state or have a prescription which I believe neither apply to the OP.
Why would he want to grow low potency weed? Why would anyone? Unless you are growing legally that is. Its like people that just buy a joints worth or a 20 bag every week. Why? Why take the risk more often when buying an ounce will not only save you money, but lowers the chances of you getting busted.
If someone got caught growing 10 plants that were very low THC, they would get just as much time as if they were growing 10 of the most potent strain in the world. The only difference is how stupid that person will feel for growing shit weed.
My advice to the OP is this....If your wife is trying to quit smoking cigs, she needs to own up to the fact that it is VERY hard to do. Also, it is so much more unhealthy than smoking pot. In my opinion, it sounds like she needs to smoke MORE. People only get "too high" and "non functioning" when they dont smoke much. Have her smoke a decent sized joint, or even a pinner EVERY DAY when she gets home. maybe 2 a night. Then after a bit she will be able to roll small joints for work. But also keep in mind that joints STINK, I personally carry a dugout with me at all times just because of that. It looks like a cigarette and doesn't leave your hands smelling like a roach. My wife recently quit smoking due to pregnancy and I will do everything in my power to keep her from starting back up. Half of my current grow is going into jars to cure just for her. She cant smoke for 2 more months so that weed will be SOOOOO good by then!
Best of luck to you and the Mrs.
KB