I can't help thinking a lot of this is just over-load.
Some kids are fine with a constant barrage of stuff to do and keep track of, and some kids need more empty space.
There's a lot going on with this kid - two households, school, siblings, activities.
It doesn't sound so much ADD-like to me, as just unwillingness to be that "on" all the time.
Though, of course it's frustrating, especially if this is a re-play of living with her dad.
If it's any help, my own dreamy kid turned into an organizing fiend at about 17.
But it doesn't teach your kid to be responsible for you to be running after her about all these different tasks.
What you need to do is back off a little, and let her realize that these are not *your* issues, but her own.
How about re-structuring things a bit?
What happens if you just leave the bag from her dad's house?
She probably has plenty of stuff to wear anyway.
So the worst result is that a batch of clothing just isn't ready for her later, because it's still in the bag.
Her problem, not yours.
Can all the spare leotards just ride around in the car, even if the bag is elsewhere?
She doesn't have all the other stuff in the bag, but you don't have to go haring off after yet another outfit.
Can you just let her go to school with an unsigned notebook?
Let her deal with the consequences at school, so that it starts mattering to her if it isn't done.
The cats, though, do need to be fed.
Maybe, she doesn't eat til they do.
No dinner, no breakfast, no leaving the house for her til cats are done.
Eventually it levels out.
I think at this age they are just gathering strength for their adolescence.