As a former "difficult student", I'd like to offer my two cents. You offered to help her and she refused your help. You need to let it go unless she comes to you looking for help and advice. Trying to teach someone who is not interested in learning a new technique is just going to leave you both frustrated.
If she is willing to try PMTS you need to make sure that you do any exercises on an extremely gentle slope, especially since she is already afraid of falling. The first time I ever tried to learn PMTS it was on rollerblades. I got on a hill that was too steep for me, lost my balance and took a hard fall. That fall was so demotivating for me that it was years before I was willing to try again with PMTS.
I had to be open to learning before I could progress. No amount of watching other talented skiers could convince me otherwise because in my head I had gone as far as I could after years of TTS lessons that went nowhere. I had decided that I just wasn't very athletic/a very good skier and I had gotten as good as I was ever going to get.
Harald mentioned that there might be something going on with her alignment. I haven't been aligned (will be having it done at my 1st green/blue camp this Feb) but I had ankle and shin pain with my boots. Again, I figured that ski boots were just uncomfortable. When first learning PMTS I couldn't figure out how to pull my feet back.
I finally went to a boot fitter to see if they could do anything to make my boots more comfortable. It turned out that my boots were way too big in the foot. I ended up getting new boots with a smaller foot volume and a larger and lower cuff to accommodate my calf. With my new boots I could finally pull my feet back and though I am still very much a beginning PMTS student (2 seasons of 10-15 days plus rollerblading in the off season) with a long way to go I am finally making progress after years of being a terminal intermediate.