Oh bless her poor little girl,I really feel for her it must be bloody awful to constantly feel like that.
I have ocd but I'm 40 and my ocd has got worse now I'm older,it was no way near as bad when I was a child,for that I'm thankful as I'm sure I cope better with it because of being older if it had been so bad when I was a child I'm sure I'd have been a nervous wreck.
We have two children that are both autistic and our DS14 also has to deal with dyspraxia on top of the asd.
Is your little girl getting any help from anywhere for the anxiety?If not then I'd start there it could make a world of difference for all of you.In the meanwhile is there anyone she can walk to school with? a friend her age or older an older sibling maybe?
Another thing that might help is her listening to music with some headphones on as she walks to school,it helps to break the conceration,therfore it could help stop the negative faults which in turn would stop the anxiety.
A lot of children and adults with anxiety,ocd,asd,ect find that listening to music not only helps them block out the sounds around them it also helps them block out many of the extra sensory things that are going on around them which in turn can stop the negative thoughts and anxiety from being able to take hold of them.
We used that technique for a couple of years with our youngest DD(now 8)before we started doing that we couldn't go into town,shops,cafes ect for a very long time.For us it worked from the very first time we tried it and she now no longer needs the music and headphones 
I've recommended it to numerous parents and so far they've all had success with it,I hope something works for your DD and yourself.