I think the sticker reward would work well. Or a surprise box reward, a box full of trinkets from the $2 shop and she gets to put her hand in an get one out when she has done a wee or poo on the toilet or potty is another way of a reward. I had a friend who fully TT her 18mth old. We were all amazed. It can definitely be done at your DD's.

Worth a try, if it's not happening, then try again in 6mths time.