My Latin sucks, I'd be the first to admit it. There may well be better choices of words, but in the end it's the emotion behind it that counts, not the sounds.
- Turn to the east. Trace a circle about you, if you will.
- Trace a pentagram, and say: 'Discipula!'
- Turn to the north, trace pentagram, say: 'Maga!'
- Turn to the west, trace pentagram, say: 'Vampyrus!'
- Turn to the south, trace pentagram, say: 'Deletrix!'
- Return to the east, say: 'Willow!'
- Visualise the pentagrams and the figure of Willow standing before you.
The words are selected to reflect different aspects of the character (and ordered in the way I felt best resonated with the elements associated with the directions), and in Latin... well, simply to add a bit of occult feel (and of course magick incantations in the show are not infrequently Latin). 'Discipula' stands for (female) student or scholar. 'Maga' is the feminine form of 'magus', which of course means magician. 'Vampyrus'... no explanation necessary (this is not a classical Latin word, of course). 'Dēlētrix' is defined in one dictionary as 'she that annihilates or destroys', reflecting here the 'Darth Rosenberg' aspect.
I considered using 'Lamia' instead of 'Vampyrus'. This is of course not the exact same creature, but it does have similar qualities, and might resonate a little better with the classical language (and it's also a feminine noun). I dunno, doesn't make all that much difference in the end, but of course the word 'vampire' does have special significance in the context.