Update: Ona Diet says in the comment below;
I'm not sure what she is wearing exactly but I did find a similar dress in a plus-size from nordstrom.com. It's a Bari Jay Lace A-Line Halter Dress in Black/Bronze. It's a great fit.
Thanks much for this. I've copied a photo of it here. It costs $178 and is described as 'Deep V-neck and shirred charmeuse waistband shape a lace A-line with a metallic satin lining.'
If anyone else recommends a sexy dress in plus sizes, please send me a photo or link.