Your daughter's case will be adjudicated in the juvenile court, if you do not already have an attorney for her you should retain one. Juveniles are not found guilty or not guilty as criminals per se but delinquent when the charges are found to be true and from there are either incarcerated or placed on probation and court supervision. No one wants this on their record so if you can hire an attorney to work with the prosecutor to get a good disposition it will be money well spent. You are a witness and not a defendant so invoking the fifth amendment does not apply. The plaintiff in a criminal case is the state with the actual victim as the state's witness of the crime, if you refuse to testify the state can hold you in contempt. An attorney can explain the options as there are a couple you might want to consider.
Whether she will get jail time depends on how serious the assault was. You do not have to press charges, that is up to the police and the district attorney. She needs a lawyer (and yes she can refuse to testify.) Whether that is the right choice depends on too many issues to discuss online, which is one of the reasons she needs a lawyer. You will have to testify if you are subpoenaed.
I am licensed in Pennsylvania. Members of my firm are licensed in various states, including Pennsylvania, New Jersey and New York. We handle cases involving personal injury (car accidents slip and falls, etc.,) medical malpractice, nursing home abuse, workers' compensation, social security disability and legal malpractice. Nothing I write on Avvo is legal advice, but instead contains general educational information. Please do not act or refrain from acting based upon what you read in anything I write on Avvo without retaining your own lawyer in your state. Also please remember that this post does not form an attorney/client relationship between you and me. If you have specific legal questions, you should contact an attorney in your state for assistance.
As a criminal defendant, your daughter has the right to assert her 5th Amendment privilege and refuse to testify. However, she should consult with an attorney about the advisability of asserting her privilege in light of the individual circumstances of her case. I might also suggest that you hire your own (separate) attorney to evaluate whether you can be compelled to testify as a witness in your daughter's trial. In some instances where the accused and alleged victim both engaged in physically aggressive behavior, the alleged victim of an assault may also have a 5th Amendment Right to remain silent.