Help please - clueless mother of the groom

[womananddog]

I need a dress for my son's wedding in July. It is a fairly informal wedding and will be outdoors (weather permitting). I am a size 18 and want something that will cover my arms.

Phase 8 is the place to go.

I like this https://www.phase-eight.com/product/reanna-pleated-dress-10009470106.html#cgid=Occasionwear&is=true&sz=60&start=0&isSecondPage=false&pid=10009470106&pos=8 but am not sure how it would look on a plump women in her 60s