My Grandmother Is 85 She Is Quit Thin And Has

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?