My daughter had one mainly at night time, or (nap time) Like yours it was the only way to settle her, she was around 4 when we broke the dummy cycle, We found being firm with her just made her want it more, We new a little boy at the time who had just given his up and we invited him around for tea, his mum had told him a story about the dummy fairy, and he explained he tried to explain to my daughter that the dummy fairy needed more dummies to help poorly children in the hospitals, and that he got a nice toy that the fairy had left him beside his pillow when he woke up the next morning, It worked for us. she never had speech problems thankfully, Good Luck.