How to measure a pregnant Bridesmaid?

I have a bridesmaid who is currently 6 almost 7 months pregnant right now. She will be 8 months post due date when my wedding occurs, but will still be breastfeeding. She breastfed her first baby until he was past one year old, I assume it will be the same with this baby. Pre-pregnant she is a size 4; right now, she is measuring a comfortable size 6 with some baby added to it. We haven't been able to get into the shop where the dresses are being ordered out of due to all appointments being booked. We measured her EXACTLY how the shop told me to and it came out this way, bust: 38, waist: 27 and hips: 38. I have asked around and they have told me to order two sizes larger than her normal size, so an 8 OR to go with the largest measurement, which is the 38. If I follow her bust size of 38, the dress size chart says she should be a 12. If I go with the hips size of 38, the dress size chart says she should be an 8. I am conflicted and confused. Please help!