The most important visual indicators that you need, as the ability is currently implemented, are:
1) How much time is left on WD
2) How much more healing is needed to cleanse WD

I think the best place for this would be on your HP party/target bar itself. One approach could be to overlay a grey/black bar on top of your HP bar when WD activates, representing the remaining amount of healing needed. As you heal the target in WD, the bar shrinks to show the HP bar underneath until it disappears. You could place a countdown timer either on the bar itself or next to it to show the time remaining.

That second piece of information, namely how much healing is still needed, would be really useful to know.