How do you tell someone no?

Tweet

I have a friend that uses anyone she can parents family friends whoever, they don't know how to tell her no, i've alreayd set my boundaries with her so she knows better than to ask me, but the others always come to me and ask for my help, I can't help much because they've already became her safety net and its hard to get someone to listen to you after all you've ever told them is yes, how would you go about, helping someone who came to you for help??