You can fire the attorney by sending her a letter of termination.  You should request a copy of your file and a refund of any unearned fees. There may be a charge for the copy of your file. It would be advisable to contact the State Bar.  Sometimes a call from the State Bar will prompt an attorney to respond.   You may have a malpractice claim against the attorney, but prior to filing the lawsuit contact the State Bar.

You should also obtain a substitution of attorney form which the court in your state may have.  Your attorney would sign the form and you would sign as temporarily being the attorney in pro per (representing yourself) until you can find another attorney.  After the form has been signed by you and your former attorney, file it with the court.  As a pro per (representing yourself) you can request a continuance of the mediation explaining to the court that you need time to find another attorney to represent you at mediation.  Your new attorney will then sign a substitution of attorney form in which you would no longer be representing yourself because the new attorney will be representing you and will be the attorney of record.