Don't respond to it in any way, COMPLETELY ignore it and it will go away eventually. If she tells her she doesn't like it,your daughter is actually just giving her the ability to push her buttons whenever she likes, so it's important that she doesn't do that. I daresay she's picked it up at nursery as some people's language is very colourful shall we say in front of their kids and kids will pick up a word like that in a trice and hold onto it if it ticks off adults as it gives them a power they don't usually have. Just ignore it and eventually it will stop being used.