Pink Cotton Candy

I found this adorable pink cotton candy dress at iamsonotcool. I love this dress and I want to buy it but I'm not sure if it will fit. It is 17 inches from armpit to armpit. That is REALLY small. There are darts but I'm not sure how much room they will add. What do you all think? I wonder what size bust would fit in this dress. I WANT IT!!! I'm kind of small but I don't know if I'm THAT small. The mod little buttons are so cute. And, I love the detail in the zig zag stitching. I have a dress practically the same style that fits great. I guess I should drag it out and measure it. That's been my best bet for finding vintage clothes that fit. I find something I already own in the same style and then compare the measurements. Well, I'm off to get the tape measure.