I feel your pain with her Paula, I too, have a little mare that is much the same as Taff. Ive had her for two years now and had I have not been so held up with a dodgy coccyx and being able to get around freely , I may have been able to do a little more with her.
She is really good one minute then realises how close she is to human contact and then freaks out. She had very limited to no handling as a youngster apart from rushing a group of broodmares into a stall to have their feet trimmed and worming done. The girl I got her from had brought her forward in leaps and bounds in trust.
It is sad to see them like this , as you only want to help and let them know they are loved
But good on you for sticking with her , cause alot of people wouldnt have given her the time that you have