She's not turning 18, a milestone signifying legal adulthood, nor is she turning 21, the legal drinking age. She is turning 19 which, by itself, has little particular significance. Since this is the case, examine her lifestyle to find the best gift for her. From study aids to help her excel academically to upgrades on the items she uses everyday, there are plenty of gifts appropriate for a young woman who is turning 19.
Many 19-year-old girls are in college, therefore a gift that will help her in her studies is a very practical decision. If her birthday falls near the beginning of a semester or term, consider volunteering to pay for her books, typically a very costly expenditure. A voice recorder or a laptop with which she can take notes are also good ideas.
Your 19-year-old will probably have a few items in her life that are a little worse for wear or are getting a little outdated, such as an old computer or a raggedy winter coat. Replace one of these items with a newer, better version. Even smaller items, like MP3 players can be updated if they are a few years old. She can decide what to do with the older item, such as selling it and earning a few extra bucks.
Money and Gift Cards
Many 19-year-old young women don't have a lot of extra money to spend. With this in mind, a gift of either money, a store gift card, or a prepaid debit card is very appreciated. If you decide to buy her a gift card, make sure it's to a store she would enjoy shopping in and has easy access to, otherwise it will likely end up forgotten in a drawer.