Sounds like it has become a prop, same thing happened with my DD and around the same age... it seems I accidentaly got her hooked on her dummy. I ended up having to help her sleep without it, because I knew it would be a long time yet before she could find it herself. It took a couple of days, but it really helped. I reintroduced it a couple months later, now she will still take it or leave it.
I started in the morning and made sure she had all her naps without it, and then did pat/shhh for the night wakings. It was a tought couple of days, but definately worth it. There is a lot of info in the props board if you are interested.
Good luck!
Jaime