A good way is to constantly cast paralysis and attack her when she's down, but if she's resistant to magic that plan goes down.
Paralysis does work on her. A master of sneak may also be able to take her down from a distance while remaining undetected. This, of course, assumes she has an average sneak skill and thus will take longer to detect you. If stealth isn't your thing, I highly recommend saving up for Apotheosis, as stated earlier.