I use 3-methods for hemming silk chiffon.
1. Machine rolled hem, using rolled hem foot - not my favorite.
2. Stay stitch hem edge - sewing a straight stitch 1/4" of edge. Trim any uneven spots. The stitch supports the chiffon. Roll that to within hem, press, stitch as straight as you possibly can - my second favorite.
3. Small zig-zag, stretching along edge for ripple - my current favorite. I prefer using a small tight zigzag, between 1 and 2 both in width and length, to using a serger. I find the serged stitch to be too heavy for my liking with silk chiffon. I am sure there are methods to lighten it up, but I am more comfortable with zigzag and its outcome.