@Roberto ********
Exactly. Besides, I'm assuming said minibus is Thai registered and while it could theoretically have picked her up in Cambodia, these services don't operate this way in order to save costs.
They simply switch transportation at the border and if you arrange a "thru ticket" the transportation waits for you. The other, more sensible option would be to just book transportation once you've crossed the border.
These "thru services" are a scam, as it's usually cheaper to do it on your own.
The only cross-border thru service I would be willing to use is a bus or van that actually crosses the border, meaning there is no change of vehicle. As soon as there is a change of vehicle, I say no.