The first one is correct and is even a common saying. If it can help you, an acceptable traduction would be something along the lines of:
She's been found ? Now that is some reassuring news !
The second one, Voilà ce qui me rassure, doesn't make sense here, though you're right in your translation. It is used to make a list, or more generally to point at something. For example, let's assume you're going on a trip and are making a list of things you didn't pack yet:
Voilà ce qui me manque pour demain:
Un sac de couchage
Or another one: you had this feeling that you had forgotten something, but you didn't know what (damn that's a crap feeling). Then, you stumble upon your old game boy and realize that's what you were missing:
Voilà ce qui me manquait !
That's/Here's what I was missing !