Been on reddit a long time but never created an account until I saw your post. Not sure how this works or if you'll even see my comments but feel I can offer you a few avenues to explore. First, I would highly recommend backing off on DSS or the police. There's no need for any of that at this stage and could potentially make things much worse for you, and more importantly your daughter.
I understand. You are at a loss and struggling. It's frightening when you have a child who acts out like an adult on a full blown rampage. And it can be so hard to remember that she's only 11 when she's in the middle of an episode.
I have been there my friend. My own son has a somewhat similar story. But before I say anything more I want you to know that my child is not yours and you will ultimately know what is best for her. From what you've stated there may be other factors at work so please understand everything I'm going to say is based on my experience, not yours. Take what you want and toss the rest.
So here we go!
First, has your child ever been diagnosed? Anxiety? Depression? ADD? ADHD? Anything like that? Not sure about the state you live in but does your child have an IEP (Individualized Education Program) in place at her school? An IEP can give you and your child access to a lot of resources that may be extremely beneficial.
What you are describing sounds a bit like ODD - Oppositional Defiance Disorder. It's a heck of thing! Are your daughter's outbursts triggered when asking her to do something else when she's happily doing another task? Or in the past at school have the outbursts come when switching tasks or when other children 'pushes her buttons or interrupts what she is up to at that moment'?
I would highly recommend reading up on ODD and as well talking with her therapist, family doctor, school psychologist and a psychiatrist as well. Having a wide range of professionals review your child will help formulate a more accurate picture of what is going on. This will become crucial, especially in terms of any potential medication that may be suggested. It may seem like seem like overkill but the kinds of medications that may be prescribed are based on studies done with adults so it's still a guessing game when it comes to these types of meds and young children. You didn't mention medications in your post so this is why I brought it up.
As a whole, these professionals can help make various recommendations on forms of therapy, counseling and or potential medication. Knowing your options will also give you, the parent, input into what may be the best options for your child. The professionals get a snapshot of what's going on. You live the movie and have read the novel a thousand times so you'll be best equipped to decide what avenues may work best.
Next, I think it's fantastic you will be attending her next therapy session! This is a big step in the right direction!
From my own experience solo therapy for my child was a complete waste of time. In fact, it made it his symptoms even worse after the sessions. It was more like handing my son a can of gasoline and asking him how big he could make the fire. It never gave him the tools on how to douse the existing flame.
I would start looking more seriously at group counseling or therapy.
The program that worked miracles for my child is called PCIT. http://pcit.phhp.ufl.edu/
It's a newer form of therapy but I'd recommend exploring it. Also, it may take some time to find a place that offers it. Very few places in my town even knew what PCIT was.
PCIT a two fold therapy/counseling where both the parents and the child are completely involved. You will be coached on everything from how to specifically speak with your child all the way on how a time out for your child works.
I quickly dug up this link that shows some of the worksheets used as well as how the therapy works.
http://pcit.ucdavis.edu/wp-content/uploads/2012/08/Section-7_PDI-Coaching.pdf
In particular take a look at 7.9 of that document. This will give you an idea about how precise this therapy gets in terms of how you speak with your child. Simple things such as "Will you please hand the the red pen" versus "Please hand me the red pen". Dropping words that may give the child a sense that they do have a choice in giving your the red pen are removed. If the command is followed praise is immediately given. "I love it when you give me the red pen immediately. Thank you!". I'm very much simplifying how this works and it took a couple months of sessions before I had any sense of mastery over it. Yes! You will also be critiqued on how you engage your child until you've got it down to memory!
From my personal experience the sessions last 1-2 hours twice per week. The adult was setup with an ear bud mic and therapy took place in a room with a one way mirror. Essentially I was coached on how to interact with my child and were corrected when we got off track. It's VERY specific!
If your child does in fact have behaviors similar to ODD this will carry all the way back to your home in terms of appropriate behavior/house rules. 'Typical' punishments (no tv, video games, ect.) don't work for a child with ODD or similar behavioral issues. It simply escalates the situation.
I was taught a time out technique called "Swoop and Go" which involves the child sitting in a time out chair that follows a very strict protocol. The technique never changes. You never adjust how it's done. I won't sugar coat it. It was really rough at first. I'm talking hours of rinse and repeat but over time I found this technique so incredible! Don't know what to do? Refer to the time out diagram. Don't know what to say? Refer to the diagram and the exact words you say. None of it varies and you as a parent can find freedom in this. It helps to alleviate your own stress, anger and anxiety. You stick to how it's done and that's it. There's no interjecting your own emotions into the situation. Removing your emotions from the situation also takes away some of the power your child has over you during a blowout. I swear my son could sense me unraveling and would step on the gas to see how fast he could get the wreck to happen. Once my emotions were out of the way and under check I was in control. This also helped me from resenting my child. I went from dealing with my child and a bucket of emotions to dealing with the situation and nothing more.
OP, take a look if you think it makes sense. If not, I apologize for the long read.
Buckle down, parent up and start telling your child you are going to tackle all of this as a team!
Regardless of the route you go she needs to understand that you are all in this together and that Mom and Dad are going to be right there with her!
You are not alone OP. There is a wonderul and happy future awaiting your child and your family! Plus, if you end up doing any of what I did you will end up with some pretty bad ass jedi parenting skills!