aww bless just try to relax about it there is no certain age where is has to be done, i also struggled with mine, at about 18-20 months i took time off work and just stayed at home to potty train, within weeks she picked it up fine, but then when we went out it was a nightmare, in a pull up she would just treat it as a nappy and not tell me when she needed the toilet, and in knickers she would ust wet herself, but like i said in the house she was fine, she started nursery at 2 and a bit and on her first day they had to change her knickers 3 times as she simply didnt tell them she needed it! but i was just persistant and kept trying, at home she only wore knickers and like others have said you just have to let them learn, they dont like to be all wet and smelly so they will soon pick it up, dont stress it really is just trial and error,
good luck xx