I'm not going to lie to you. Many of us who write strong female characters have begun to wince when we're asked to talk about them at panels or during an interview. It's not because being a strong female is a trend that has passed, but because it was never a trend in the first place.
Women were strong before Katniss picked up a bow or Tris jumped off a train. Read The Long Winter by Laura Ingalls Wilder - a true story - and you'll see a young girl braiding sheaves of straw together until her hands bleed so that her family has something to burn in their stove to ward off the bitter temperatures. Read that book as an adult and you'll understand that the family is dying, slowly starving to death while malnutrition and ennui sets in.
I dabble in genealogy as a hobby, and have traced my German line back to the 1500s. There I found a woman who gave birth to 15 children - and outlived all but two of them. I ran the dates, and in one week she lost two adolescent daughters (due to an illness in the home, I assume), gave birth a few days later, then lost the infant the next week.
She kept going.
There were seven other children still at home that needed care. She went on to raise them, and deliver more healthy children that grew into adulthood. She lived to be nearly 100 - certainly an accomplishment in the 1500's - and buried all but two of the children she gave birth to.
I bring up this ancestor from 500 years ago when I'm asked about writing strong female characters. This mother of fifteen didn't know about YA literature - in fact, she probably couldn't read - but I'm pretty sure she would have laughed at the idea of strong women being a trend.
Women were strong then.
Women are strong now.
Women will continue to be strong.