If you think you're doing your friend a big favor by buying a really expensive item that she's been lusting over, there might be one drawback that you probably didn't know about. It's called the "aesthetic incongruity resolution" and it gives people the urge to buy things to match up with the nicer item, according to the Boston Globe.
For example, if your closet has no designer pickings, getting a brand-new Balenciaga from your pal might upset the balance. You might use it as an excuse to get a pair of expensive Manolos to "even things out" in your wardrobe.
There are plenty of gifts that won't cause this designer distortion in your friend's life. If you want to gift your friend with something meaningful, consider experience gifts such as tickets to the theater or crafty presents like scrapbooks or framed pictures.