it 'can' be done with 2 persons, the other has to be a shaman or warlock, and you need good communication and gear (not recommended)
been a while since i did it, but, if i remember correctly:
someone else needs to tank her, and you needs to be the closest person to the tank (only you and the tank goes in the rest stays behind)
when going in it is important that you have shadow's edge equipped
pray that you get 1. bite (afaik it should go to the one highest on threat but it didn't always when I got it, which is why more people = easier)
whenever you have to bite you have to have shadow's edge equipped
if you let people die after they've been bitten you will not get overwhelmed with vampires, but keep in mind that they heal when they deal dmg
basically, if you get a couple of people, have shadow's edge equipped all the time, go in as 2. person
after you've gotten bitten, let people who have been bitten die and CR/ankh/SS them (the more you have the easier) and just dps her slowly
sucks to kill her before you've done 3. bite
hope this helps
ps. I did this 4-man back when I did it (patch 5.0 all with half blues/LFR gear) were almost able to do it 3, but we wiped a couple of times and it was easier to get a fourth guy