How do I not mess up this beautiful dress? (sewing question)

My co-worker is having a baby shower this weekend and bought a dress that’s too long. I offered to shorten it since I’m the only one with some sewing experience. I usually just do my own stuff though so I don’t feel bad if it looks like hell.

The dress is fancy and shiny and 100% polyester. She says it’s not stretchy. Any tips for tension, stitch length, etc.?

Thanks!