The phrase "how relieving" is correct and usable in written English.
You can use it to describe a feeling of relief. For example: "When I finally got the job offer, it was how relieving!".
How relieved was she now?
How relieved she must be to be free of The Apprentice (BBC1).
"They frequently tell me how relieved they are to know we're there for them".
On the other, it's about how easy it is to strip people down to their core, and how relieved they'll be if you do.
How relieved are you that you didn't bruise your libido with a trip to "Scoring" or "Campus Panty Raids" or "The Starlets"?
She and her son were talking about how relieved they were to have electricity again Wednesday afternoon when the lights flicked off around them.
For instance, we remembered how relieved we were when we realized that fear was not going to interfere with our jobs.
Mostly you're thinking about how angry you felt at work and about how relieved you are to have a way of legally avenging yourself.
He told Westminster coroner's court how relieved he was when the gunman began lowering the weapon, only to move it upwards again.
Imagine how relieved poor old Oedipus would have been if the worst he'd had to face was an airborne shoe or two.
Early on, Terai told me, he was struck by the large number of men who wept at divorce ceremonies—"The women are usually O.K., but the men are bawling," he said and by how relieved they looked afterward.
