Women love gifts more than anyone on earth. They would prefer well chosen, nice and necessary gifts, reflecting their nature as a mirror.
The famous phrase that 'diamonds are the best girls' friends' is a well-known fact open to question. Every woman might dream of a beautiful brilliant necklace deep inside her soul, but in fact, such a gift is likely to be too obligating to accept. Expensive 'gifts for her' are better be given by husbands, fathers or other relatives, otherwise those presents are supposed to be ambiguous and confusing. Although every girl is free to decide the matter to her own discretion.
Women would really appreciate flowers, perfumes, good cosmetics, clothes, accessories and beautiful erotic lingerie. Anyone is welcome to present flowers as a 'gift for her' on any occasion. Each girl has her own floral preferences, but she'll be glad to receive any type of flowers. Just don't cling to read roses. They are traditionally given to married women, and nowadays are too abused to keep their natural charm.
High-quality cosmetics will be a very good girl gift. One should be more careful with perfumes, as every woman has her favorite fragrances, and is quiet loyal to them. The same thing with accessories, though if you always rely on your good taste, you may go for it.
Clothes and lingerie as a 'gift for her' should be given only by close people, not much because they know the tastes and preferences, but because they have great confidence in sizes.
These are the most complicate issues. Who told you should redouble difficulties? CD with her favorite music, some widely advertised blockbuster on DVD, a good book, a plant in a pot, photo frames, a purse, or electrical devices will be appropriate as a necessary and wishful gift for her.
You may either try something original, humorous or practical. Check her hobbies and interests up, add a little bit of imagination. The one who seeks always finds.