Modern girl can be a someone who likes to party a lot, who likes to blow away money in credit cards, believes more on luxurious life, likes to drink, lacks responsibility of her actions, changes boy friend every week/month. I can be wrong on using right terms but the point is obvious what I am trying to imply. Also, this is a subjective matter. Everybody will have their own perspective. Anything good to someone may not be good to another.