My Daughter, Aged 15 Seems To Have A Discolored Area

My Daughter, aged 15 seems to have a discolored area along her spine, in just above her hips, ( about 3 inches long). she doesn't complain of any pain....
there have been no injuries...
she used to have 2 un joined spots that we thought were birthmarks, but now they seem to have joined.

this area looks like a bruise.... slightly longer than my index finger.

any ideas?