If you and the father are still together and parent together, what is this business about "unsupervised visits"? Do you know who filed a complaint with DCF?
You need to CALL an attorney. Any decent attorney will not charge you simply to listen to your story and decide if s/he can help you. There seem to be a lot of facts missing. Talking in person to a lawyer who will be able to ask clarifying questions in real time is important with time-sensitive cases like this.
Use the "Find a Lawyer" guide above to find one or more qualified child custody lawyers in your area. I'm sure you can get one on the phone who can meet with you today or tomorrow.
DCF wants to "screen out" the case because the grandmother having gotten temporary custody means that DCF does not currently have any "protective concerns" about your daughter. DCF apparently believes (may have even suggested) that the grandmother's petition solved the abuse or neglect that she reported to them.
Schedule an appointment with an attorney who will represent you in the Probate and Family Court proceeding that the grandmother filed. If you are unable to do that before 8:30 tomorrow morning, go to the court listed on the copy of the papers you received from your daughter's school. Go to the Probate or Guardianship department in the Register's office of that court. Show them the papers you have. Tell them you are the mother, that the motion is a lie and that you object to the petition. Ask to go in front of the judge to try to get your daughter back or at least to have an actual hearing where the grandmother has to convince the judge that your daughter needs an emergency, temporary guardianship.
If the court where the case was filed has an attorney of the day on duty when you are there, you can get the papers to bring with you for a free consultation with that volunteer attorney. The attorney of the day can help you fill out and file an objection, how to schedule a hearing on your objection and how to notify the grandmother so that she will be required to be in court to defend her petition and motion.
You can also ask that your daughter be given a court appointed attorney.
Then be sure you hire an attorney to represent you at the hearing that you schedule and start gathering all the evidence and witnesses you can to testify and document that you take good care of your daughter and that she is not in any danger that she needs to be protected from by being in her grandmother's custody.
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The grandmother must have filed for custody, along with a sworn statement alleging facts supporting such an emergency order. When you examine this document, you will probably find quite a bit that doesn't seem true. There will be a hearing within a very short time to see whether the temporary custody order should be extended. Because this is a private party case, not brought by DCF, you are not entitled to appointed counsel even if you are low-income. You will need to hire a lawyer, and you should do it ASAP. Your county bar association or Mass. Bar Association can give you some names of family lawyers who may be able to help you.
Disclaimer: This site exists to provide information only. It is not legal advice. Answering your question does not create an attorney-client relationship. I am a Massachusetts lawyer. Any information provided on this site does not, except as explicitly stated, imply familiarity with laws or procedures peculiar to your state which may differ from those where I practice.