I've read that if you're running as your primary cardio exercise, you won't need to put
as much effort into strength training your lower body, but you should do it. From what I understand, running tends to really develop the quadriceps, and I've read that to help yourself stay injury free it's good for female runners to make sure they strength train their hamstrings and inner thighs to balance out the increase in the other muscles. Hope this helps a bit.