In pve the healer is in the DPS rotation, though its not usually as ambitious as the dps spec classes. When needed I swap key profiles and the healer is out of the the dps rotation. To be clear the healer is idle at this stage unless I do something with her. Often this could be as simple as a /targetraid fixit grind or some prayer spamming or whatever.

Normally I shift her out of dps, do a castsequence of a 'fixup tank' and then swap back. I think a lot of people that run with a dedicated healer do this but have it as two keybinds so they press a{1,1,1,1} for full dps and b{1,1,1,2} for mixed dps on the multiplexer.