I see why Nandi is not good at all (maybe the saving grace only being her stats). But anyways, let's go to the math I used:
Each attack gives 10 burst. With Nandi, it would be 12. In hypothesis, given one kami who attacks only once each turn and never gets attacked by the enemy, that character would burst every 10 turns. With Nandi, she'd burst every 9 (12x9) turns.
The Zeal from Yule Goat gives 5 burst every turn, during 3 turns, so lets just consider it a +15 burst effect. If Nandi would increase the Zeal to 6 burst each turn (which I don't know whether she does), it would be +18 burst. The hipothetical kami that never does combos would burst every 7 turns (12x7 +18). Considering combos and enemies who aren't immobille, it is realistically a FB every 6, 5 or even 3 turns (2 triple attacks or 3 doubles, +boosted Zeal).