I would not sign a lease in NYC unless and until you get permission from the Judge to make the move. If she is denied permission, she will still be obligated on the lease, and will be expected to pay regardless of her situation. It is likely that the Probation Dept. will notify the State of the dirty drug test, and they will likely file a Petition to Revoke her Probation in the Circuit Court.
Of course, if you are truly serious about the move, you should at least be prepared to show the Judge that you are capable of signing the lease immediately upon getting the approval for the move, and only if the Judge agrees not to violate your probation for the dirty drop.
You should retain an attorney to assist you in court on the motion to permit the move, and/or to defend any petition to revoke your probation should one be filed against you.