At least they aren't also stipulating that the kids move their instruments while wearing roller skates. Schools sure don't make it easy for those of us who play large instruments..
I started on 'cello in public elementary school and we had to deal with similar schlepping and unsecured storage issues. Brings back memories of trudging along in the freezing, rainy weather with my rental Kay 'cello in its cheesy canvas bag. Coming back to the instrument to find the case open, music strewn about, a couple of times. Getting in and out of the bus without destroying the thing. Walking down the hall while various miscreants hurl towards you, chasing each other.
I would gently, lovingly, and clearly impress on your daughter what was impressed on me...protect the bridge area and the neck from impact. Don't lay the instrument on its back, lay it on its side, with the bridge facing away from traffic - ideally, against a wall. You might also get her in the habit of taking the bow out of the case before unpacking the bass, so you don't snap the bow into kindling. And of course, try to protect the bass from falling from a standing position.
You might also do well to get her an inexpensive bow case to keep from breaking the stick, should she forget to remove the bow from the canvas bass case one day before pulling out her instrument (sort of inevitable, I think, for kids). Or, you can cob something together that will work as a bow case; when I was a kid, I used an old mailing tube that I had pulled out of the trash.
+1 to what Uncletoad said, the music teacher may be a good ally in this affair. The other kids certainly won't get the delicacy of her instrument, at all.
When I switched to bass in high school I worked out an arrangement (read: begged for help) with the music teacher, who allowed me to store my bass in various places away from the destructive crowd. At one point, in a different school, a friendly janitor did the same thing for my 'cello, letting me store it a low-traffic space. So, maybe somebody at school can help with some sort of special treatment for such an unwieldy, delicate instrument. Rules are great, but storing a bass is clearly tougher than storing a trumpet case and may require a bit more flexibility from the school. All one needs is one reasonable, helpful teacher or custodian.
In school, I carried my bass in the soft case, in front of me with the bridge facing "in." Same position for going down steps or off the school bus. It usually parted the seas of kids and helped me get through doorways without damage.
Going up stairs, I either carried it leaned against my back and hip (with the bridge in) or when going into the school bus, sort of next to me, on its side, again, and always, with the bridge facing "in." I like the shoulder strap but only if I can carry the bass a little to one side, with the bridge "in" towards one hip.
Finally, are you renting the bass? Any insurance you can get with the rental shop? Can they show your girl (or you) how to set the bridge and right the soundpost?
