Meghan wrote an answer about Canada Goose Chilliwack Bomber - Women's on February 12, 2010
I'm almost 5'5 and 118 pounds. I just bought a Women's CG Chilliwack Parka in Brown - size S. I bought the jacket for function not fashion and the size S doesn't ride up my back, which the Chilliwack is known for, and I have lots of room in the sleeves to pull the cuff over my mitts.
Where it is big is through the body and chest, easily 4-6 inchs of overlap. If you want a tight, city jacket and don't mind it sitting high on the waist I would recommend the XS. if you are looking for a jacket to wear while doing winter sports, to feel warm and cozy on those extremely cold winter days go for the S.
NOTE: I haven't tried on the XS to compare it to my S.