Here is what could happen if she wears long pants, long top and a head covering.
The teacher wants her to run a mile and its over 90 with high humidity. The girl overheats, passes out and dies. The school will be sued.
As the possibility of a law suit now is much lower I guess.
The right 'warm up' suit will let you perspire, evaporate and cool just fine.
If the school rightfully stipulates a health and/or safety reason, then I'll go with the school. I just don't like arbitrary school rules.
It'll take em 3 days to re-write the policy to make it make real sense - from a safety, freedom of movement and health standpoint.