The tension you have in your leg is due to 1 of 2 things. 1 is that there are some things in your life other than your back that are bothering you and the body is in response, usually called stress. Check out an acupuncture chart and look to see where the gall bladder and Urinary Bladder channels run. Gall bladder channel runs up the side of the body and when we have stress everything along that channel contracts. you will see on the head its the same place we get headaches
GB 30 has tension in your case so have someone stick their elbow in it until the pain subsides also consider GB 21 this will help tension move out of the body.
Then afterwards try the stretch again, see if it has helped.
There is a point called weizhong Urinary Bladder 40. have your girl stick her thumbs in that point for about 2 timed minutes, longer is better. this will help the pressure on the lower back.
My teacher has just written a book that explains why you get back pain and what to do about it, I will let you know when its ready if you like.
But for now these 2 things will help your pain. Your leg sticks up because of the tension in the hip pulling on the muscle, relax it and you will find your back will also relax. It has either stemmed from a weakness in the back or just plain old stress but now stretch and things will get better. Hamstrings and Glutes and breathe with both.
good luck!
Jedd