Looking at getting dd (15) a couple of t-shirts from Hollister online. Going by their size guide a S is between a 8-10 and a M between a 10-12. I'd say a size 10 in women's from New Look fits dd nicely, not tight fitting, not too baggy, a 12 from New Look would be probably a bit baggy and an 8 maybe just close fitting.
How true to size is Hollister? I, thinking a S (8-10) would be best for dd as its not a crop top or tight fitting t-shirt just a normal t-shirt.