I'm so impressed by this cosplay. This is really how I'd imagine Cap as a woman. I've been tearing at my hair from all the flimsy interpretations with short skirts and the unarranged curly wigs that to me seem closer to Supergirl, but this, this is it, because Captain America is, female or male, a super SOLDIER and should in my opinion not look like his/her own showgirls. Love it.
The shoulder pads? They look a lore more complex then they actually are!
They are actually a fabric and craft foam sandwich. So what you would do is first cut the shapes if the shoulder parts out, then cut the smaller detailing pieces out. When you glue the smaller pieces on to the big pieces, only do enough to hold them in place, avoiding the edges. (While you are sewing, if you hit any of the glue, it will gum up your machine and not sew) Then trace off the full shoulder piece on to fabric, making them slightly larger. I choose to do a top and bottom, but you don't need too, it just looks cleaner if you do.
What you need now is spray adhesive. You spray a light layer on your detailed side, then carefully place the fabric on top, making sure you do not get any bubbles. Then take the handles of your scissors, and rub that in between all the raised sections to make sure it sticks to the bottom layer of the foam too. You do not have to attach the back layer at this point.
Then change your machine's foot over to a zipper/piping foot, and carefully sew around all the edges of the raised bits. This will lock them in place, and make them look nice and clean.
Once all that is done, you can attach the back piece of farbic, and finish off what ever you are putting the raised bits on however you want to.