Your daughter has a right under Minnesota law to use a reasonable amount of force to come to the defense of another person who is being assaulted. The legal issue in the case will be whether or not your daughter's use of a club agaisnt the attacker was a reasonable use of force. The prosecution has already filed a criminal complaint and charged your daughter with a felony offense. This means that a judge has already made an initial finding of probable cause based on his review of the criminal complaint.
A defendant in a criminal case has a right to file a motion to dismiss the felony charge against your daughter for lack of probable cause to believe that she in fact committed the charged offense. If the motion is denied, your daughter has a right to assert defense of another at a jury trial. The state will need to convince all 12 jurors beyond a reasonable doubt of all of the elements of the criminal offense before you daughter can be convicted of the felony.
My advice is to immediately retain an an experienced criminal defense attorney to defend her freedom and reputation. Call criminal defense attorney Robert J. Shane for a free phone consultaton at (612) 339-1024.