Does she really need to do so many activites? The impression I got from your post is various clubs, swimming, bikeability, piano. When does she get time to chill and do her homework and a relaxed frame of mind.
She doesn't do loads of activities, most of these are school things.
Swimming - she has swimming lessons once a week with her school until the end of this term
PE twice a week
For swimming and PE she doesn't keep kit in school, they're sent back home. Every week the kits get washed, bags packed and left for her to take to school, she just has to check her planner and pick up the bag
Bikeability - bike proficiency test with school, once a week for the next 6 weeks. Her whole class does it
Piano lesson - with the school music service (she's supposed to do 10 minutes practice a day at home)
2 school-run after school clubs until 3.30pm and once a week she does Scouts.
Homework-wise:
Spellings
1 times table sheet a week
a short 10 minute literacy worksheet 2 or 3 times a week
short 2 question maths worksheet 2 or 3 times a week
reading
a project every half term (i.e. design a theme park or something like that)
She's just forgetful. Her head is in the clouds, is too worried about her friends knocking for her or whether she can go to the park after school. After school she's so busy gossiping with her mates she forgets to bring her homework home with her. Her teachers aren't concerned about anything, she's doing well, she's just prone to airy-fairy-ness
Yesterday morning, her friends knocked, I handed her her lunch, reminded her she needed her bike. Big rush to see her friends, much giggling and chatting. I followed her out of the house 2 minutes later where I found her lunchbox on the floor in the hall where she'd put it down to open the front door (it's a 2 handed job) and her bike still in the carport. I came back from the school run to find her waterbottle on the bonnet of our car, I assume she'd put it down for some reason and then walked off without it
Every morning we have the same conversation:
me - have you checked your planner?
DD - yes
me - what have you got today? have you got every thing you need?
DD - yes, it's swimming/PE/got to hand in X homework
me - have you got it all ready to go?
DD - yes
2 minutes later, I find the homework on the floor of the bathroom, or her kit on the floor in the hall. I think I'm going to start stapling this stuff to her 
Or, I'll sort bookbags when she gets home and find she's managed to remember to take it, but forgotten to hand it in
Every evening I remind her to check her planner, what's got to be handed in, is it in her bag ready for the next day, etc, etc
I've tried making it easy for her, I do take lunch/homework/kit/etc in for her when I can, but sometimes I'm out/at work/etc so it's not always possible, and actually, I think she should be responsible for this stuff.
Hopefully a few short sharp shocks from school will focus her a bit