On Bally bingos I'm rarely stumped - but never worked on any of these flash games.
The very few that I've inspected the internals of - appear to just have a mixer, a few relays, a couple of steppers, a reflex unit (I think), meters and a replay counter. (Rather empty I thought).
All bingos have a mixer (which VERY VERY rarely gives any trouble ... ever) but they have a way more internal units than any other coin-op games I've ever encountered.
I'm guessing a slow, careful shotgun cleaning/checking/detailed inspection shop-out would likely get her going even if you're unable to locate a schematic ... (if nothing's been removed that is).