I am 5'2" and wishing I was 110 lb!

Rosie is longer than Bella and weighs 5 1/2 lb. The small is plenty big enough for her. And I think it still keeps it looking more "purse like". I sneak Rosie is all over the place. Never ever has anyone had a reason to question my "purse". I really think you would be just fine with the small.