Seconded, except you actually want an encounter with 2-3 Goblins, because after spamming Martyr's Call enough, Viv also gets a rapture every time she gets hit.
But yeah, it's nearly impossible to gain enough rapture through regular gameplay, either the enemies die too fast, or she dies too fast. Allowing her to gain > 100% rapture per instance might help? Or possibly just cut all rapture thresholds past the first in half?