you can easily see she is really feeling it. Just watch how she humps starting around 2 minutes. She is doing it with the exact fucking rhythm she needs to reach orgasm. When a woman does that, guys, just don't change a thing... just let her go... she is really close and it won't take long for her to get off!
For me it is not a question of letting her cum, it would be making her cum by fucking her missionary like that, I would have blown my load when she started thrusting up her hips and wriggling her pelvis. I also cough immediately after orgasming.