Our guild seems to have good days and bad days with Lady Deathwhisper. Our first kill was before the nerf and we were so proud of ourselves, then we had a few times where it took us quite a few goes to get her. I tend to think it's more of a DPS problem than a healing problem, and with shamans/druids/mages around there should be no shortage of decurses.
Healing setup should be 6-7 healers (6 if all mainspecs, 7 if we have a couple of offspecs), and I usually split them per side (3 per), with someone healing up the back for the tank on the stairs. I usually put a druid there and leave priests and pallies on the sides healing the tanks. Most of the ranged only take damage from the Death and Decay or a couple of shadowbolts from Deathwhisper and shouldn't really be getting agro from the mobs if the tanks are doing their job. Oh and sometimes the occasional MC'd person will do a tonne of damage to some poor healer or squishie. But the hardest part is the melee, we always seem to lose a couple of melee every time we do this fight. Shady, Moo, Kelborn are the usual deaths, and I'm not sure why that is - is it pulling agro from tanks or getting some sort of cleave? Anyway, so side healing tends to get intensive mainly on melee so priests and shamans seem to do well there.
Decursing is really important in this fight,the Curse of Torpor increases ability cooldowns by 15 seconds. Remove them quickly or you'll have vent full of whingers saying "Curse on XXX" (Client and Shady being the most vocal about their curses - rarely are they on for more than 3 seconds because most of use remove the curse and with lag between the curse happening, saying it on vent, then me doing it... most of the time by the time they say it someone has already removed it and I find it REALLY annoying...)
During phase 2 when the mana shield is down, need healers on the tanks (probably at least 2-3) and the tanks will be switching every now and then because of a debuff that makes them lose threat generation or something. The raid takes damage from frostbolts (some of which can be interrupted by melee), death and decay, and ghosts blowing up (though hope there aren't many of these - they do like 28k damage so most people will die, so ran damn you RUN!).