I too wonder if she may have some sensory processing issues. A preference for spinning and swinging can be a sign of a sensory seeker (as can the stroking of your hair/face). I found
www.sensory-processing-disorder.com and
www.sinetwork.org very helpful in explaining these issues. Some kids are sensory seekers, some are avoiders and many do some of both.
If your dd is dealing with some sensory issues, I would interpret what you describe like this: she is working really hard during the day to keep it together in a sensory overload environment and then when she gets home and relaxes that is where you see the meltdowns. For my ds, understanding his sensory issues was unbelievably helpful to me. If you realize how overwhelming the world can be sensory wise to them, then it makes the meltdowns make more sense and you also realize just how much self control they are putting forth in order to keep it together as much as they do.(And how often they are told they aren't controlling themselves because the time they spend controlling goes unnoticed). It is also helpful because the answers to these problems are not behavioral, they are physical. So for my DS, OT helped alot but also engaging in certain kinds of regular physical activity is mentally soothing to him. We have recently discovered a kid's sports training class that works really well for him. And when he misses a class I can see it in his behavior.
This is not to say you should excuse the behavior, but I think it helps to understand where it's coming from and attempting some prevention techniques. A good "sensory diet" may cut down on her tantrums if they are sensory related. An OT can get you on the right path with this. I would definitely explore this possiblity.
