If you just can't seem to find the right gift for your sister for her birthday, you might be trying too hard. Take a look at what she already has and make note of what she could use - this will make shopping a lot easier.
Looking for a gift that will wow her? Consider picking up blinc's tube mascara for your darling sibling. This formula is designed to give her long lashes and volume that can't be beat with a drug store brand. If you want to make her birthday extra special, throw in a couple of liquid eyeliners as well. It won't run or smudge throughout the day, which is something every woman can appreciate.
If your sister already has a full cosmetics bag, think about getting her something else she can use on a daily basis to pamper herself. For instance, buy her a cooling eye mask to get rid of dark circles or a pair of fuzzy slippers she can wear after a long day at work.
Whatever you decide to go with, putting thought into your gift is what will count - and your sister is sure to appreciate the gesture, regardless of what's in the pretty box.