Quick and dirty edit

I put the feet running on a level ground. I'm not sure that's what you wanted but before they were shifting around rather randomly.
I tried to have the feet move at a somewhat constant speed on the ground.
I added the frame where the foot hits the ground.
I'm not so happy about the pendulum movement of the leg going forward, it's a bit jerky.
The rest of the animation is pretty much untouched and not as smooth because I move things around so much.
I've pretty much only addressed the feet.
The leather strap on her leg is there to make the legs distinguishable.
I think something like that is needed or else it looks like a 4 frame animation.
Heelstrike debate
The main reason for having a heelstrike is so you catch the moment of contact.
Anyone can make a
google image search on "running" and make up their own mind on the subject.
I haven't researched barefoot or running in sandals but the evidence you provide is good enough for me.
But don't the athletic runners land on the front cushion of the foot.
In that case a proper animation should catch that moment not when the whole foot is in the ground.