It looks like broken blood vessels down my daughter leg (from knee to foot, in about 1 1/2 - 2 " strip)and she hasn't banged or scraped her leg. what could be going on?

That can be: Difficult to say but it may be a coagulation issue. I would see doc.

Petechia: The common causes of petechia are trauma, which usually is a result of a tourniquet type but maybe due to any trauma. Or due to a deficiency in playlet number or function called itp or due to a more serious Meningococcal infection it also could be do to medications. The key is to observe for spread if the petechia or signs of illness. If that happens see a doctor asap.