If allowed in the University, go in and talk to the mage. He will tell you to talk to a man in Skingrad. Do as he says and run errands for whoever you need to talk to. You will eventually be allowed to get rid of your Vampiricy.
The Vampiricy cure does work, but if you have completed the game and closed all the Oblivion Gates, you won't have access to fresh Bloodgrass (which is needed for the cure). Also, if you purchase it, she will not take it. If you have completed the game, try to stay away from vampires.
The following is a temporary cure for vampirism. If you have found that the witch still refuses your Bloodgrass, go to the cave close to her home (Wenderbek Cave). Wait there until 5 a.m. then go directly to the witch's house (Drakelowe). She should be asleep. While sneaking, go over to her and feed, then sneak out. You will find that you are in daylight. If you rest or sleep you will have to repeat the process.