You have posted lots about giving in when she kicks off. Whatever condition your child has, you are going to make life a great deal harder for yourself by trying to say no to something or get her to do something and then allowing her to make you give in by escalating her behaviour.
Your DD needs you to give her firm, clear, consistent boundaries. If you are willing to give in to her, don't say no in the first place. Just do what she wants. If you say no, stick to that and do not change your mind, no matter how much she screams or shouts.
If she has Autism, she may not easily see other people's needs or points of view but that doesn't mean she is incapable of understanding them. Raise your expectations of her. If you are in pain and she makes demands of you, just keep explaining why you cannot do what she wants over and over again. Later on, reflect on it with her and explain again. Let her know what you expect of her at those times and why. Don't give in and go running around after her and don't get cross with her because you've done that. If you give in, be cross with yourself, not her because you're the one giving mixed messages.
I have two DDs with AS and I have an acquaintance with a DS who also has AS. My DDs have been taught that they can kick off as much as they like, they will not make me change my decisions. They have meltdowns but they happen unexpectedly when they are overloaded in some way and are not a method of getting what they want. Meltdowns aren't punished but they also aren't rewarded and they have to help make amends for any damage later.
The other lady will say to me that she has to give her DS x or y when he demands it or he will have a meltdown. She's done this since he was 2. He is now 12 and, most of the time, he doesn't have a meltdown. He is in complete control. He has a house-trashing tantrum which stops the moment she gives in to him. The older he gets, the more control he has over their family life and the less she's prepared to challenge him because he's getting bigger and stronger and can inflict more damage.
Children need the adults to be in control of their lives. They feel anxious if that isn't happening. Although they fight to have control, what they are really fighting for is to find the point at which you will take it. At that point they feel more secure, especially if that point is consistent. You may find that, if you give your DD more consistent boundaries, her tics and other signs of OCD reduce a little.
Ask your school or family support worker for details of parenting courses. There are usually plenty around. If the ones run by CAMHS are the only option, go on them anyway. The Triple P course for parents of children with additional needs is probably what they are offering and I think it would be perfect for you. If you go one one, be honest with yourself and don't look for excuses to validate your desire to give in. Make a new start and be firm, clear and consistent so your DD learns when she is about to cross the line and has a choice about whether to do it or not.