I was in a PuG run of Shattered Halls with Kitty, that took me over 4 hours to even get somewhere...
finnally, when we had a fire mage, me ( healing ) kity, a druid and a shadow priest, DPS was crazy and i only had to heal the tank who was copping the beating....
it was insane....
so dont think that a shadow priest isnt a capable healer, if they're on DPS, and someone else is MH, you will be fine