Keep in mind, with all the advice that "good healers DPS", that the OP was leveling towards 30, running a level 28 dungeon. The implication is she's a new-ish healer and she's probably running that dungeon for the first time. At those levels, with the sort of haphazard gearing she probably has*, trying too hard to DPS is a recipe for running out of mana.
Endgame is one thing. You're running the same content over and over. You're used to the fights. You know when you can switch stances and start lobbing out damage and when you have to focus on healing. Low level? I'd far prefer to run dungeons at those levels with a healer who simply heals competently.
*No offense intended - I certainly don't spend a bunch of cash on solid gear for those levels, either.
Endgame is one thing. You're running the same content over and over. You're used to the fights. You know when you can switch stances and start lobbing out damage and when you have to focus on healing. Low level? I'd far prefer to run dungeons at those levels with a healer who simply heals competently.
*No offense intended - I certainly don't spend a bunch of cash on solid gear for those levels, either.
