I tried to get rid of DD's soother when she was about 1 - massive fail, I ended up giving it back to her. The trouble with older babies/ toddlers is that the soother is a real comfort item now, not a prop like it can be when they are younger. It's actually good that she is only having it for sleep times as that is half the battle. In my experience you need to get rid of it when they are under 6 months or leave it until they can understand that it's going, my DD had just turned 3 when hers went.
The way we got rid of it was to limit it to sleep times only and then the dummy fairy came and took them after a good few months of mentioning it and talking about it, she got a toy in exchange. As your LO is only having it for sleep I think the only way to get rid of it is cold turkey, you just need to throw them all out and ride out a few tough days/ nights while she adjusts. You can try and introduce another lovie/ toy when you do, sleep with something for a few nights first so it smells of you and will be more comforting for her.
If there is no medical or health reason for getting rid of it though, I would wait until she is older - I'm a chicken like that
Laura