There’s a moment, right before the webbing hits her when you can see Gwen accept her fate. In that moment she closes her eyes and you can see in the way she opens her mouth that she knows Peter isn’t going to catch her. In that moment Gwen Stacy is falling and she accepts her death because it was her choice. She doesn’t get to go to Oxford or kiss Peter again. She won’t ever get another chance to ruffle her brothers hair or ace a test . Right there you can see Gwen realize that her life is over, and that Peter didn’t get to her in time. It was exactly what her father didn’t want to happen, and maybe a little part of her always knew that it would end this way because dating Peter was so dangerous, but to her he was worth it. Like she said, she loved Spider-man but she loved Peter Parker more even if it meant free falling to her death. Right in that moment you can watch Gwen Stacy close her eyes and realize that even if Peter caught her one hundred times before, this time he didn’t and she’s bracing for impact.