If you're buying for a goth, what do you buy? Well what about accessories? After all if she's a woman she's going to need a bag isn't she?
A bag like the one pictured may be suitable or else you could look at purchasing a coffin shaped bag which look really awesome and are gothic inspired. You can check out a range of them at Coffin Shaped Bags including my favorite one.
If you don't fancy giving a bag then you could look at giving he or she some gothic jewelry - there are some great pieces available from pewter gothic jewelry such as the selection available at Pewter Gothic Vampire Pendants to the more unique take on gothic jewelry that's offered at Unique Gothic Necklaces - the necklaces in this selection are all silver and are only available online.
If the goth that you're buying for has an iphone or an ipad then they might be interested in a case for it. There are a great selection of Gothic iPhone Cases for both the iphone 3 and 4 available as well as some great gothic designs for the ipad available at Gothic iPad Cases.
Finally, I have to say go with a tee - it doesn't matter who you are there are always t-shirts that are suitable and these include some great gothic designs as well such as this one -
There are lots more gothic tees available at Zazzle including long and short t-shirts, you're bound to find one that suits the person you're buying for.