I have freehanded crochet shrugs for myself and others and there are only a few things you need. 1) Measure the bride’s upper arm circumference and add 2"- 3" depending on whether she wants it tight or loose. (You can also measure a favorite shirt, but I still add 1" to this measurement). 2) Measure across the back the length the shrug will need to be (elbow to elbow?) 3) Measure from shoulder to shoulder - across the back (or shoulder seam to shoulder seam on an comfortable shirt).
Then knit a rectangle as wide as the first measurement in whatever stitch you like. Make the rectangle as long as the second measurement. When you have reached the desired length, you then fold it in half width-wise (so you have a very narrow, long rectangle) and seam the edges from the each outside edge toward the middle, leaving a hole in the center the is the length of your third measurement. IM or email me if you need clarification. You can stop at this point.
You can also pick up the stitches around the opening with a circular needles and make a decorative border in knit or crochet around the edge. Some people do a ribbing, I like a crochet edge. Just do whatever suits the occasion and your mood.