my grandmother is 85 she is quit thin and has been on blood pressure medication for years. she just banged her shin and now has a blast blister thats roughly an inch around and about a half inch raised. it immediately turned dark purple and the bluster was immediate as well she experienced a hiring sensation at the time if injury. I have raised her leg and put a sift ice pack on it. is there more cause for concern? do I need to be worried about blood clots?