I'm sorry, it IS a scam. If they write back, they'll probably have some sort of song and dance about how they're missionaries just sent to Africa (you said Cameroon, but it could have been Sierra Leone or Nigeria, too) and that "this just isn't a good place" for the baby. So they're willing to send her back to the States to a good home.
Ex-CUUUUUUse me, but how would they know if you're a "good home" or a stinking puppy mill?
Then they'll add air freight from XYZ airport to the airport closest to your home. Send them the money and they'll send you the puppy.
RIIIIIIght! Not gonna happen. Do you have any idea of the paperwork Customs would want, let alone Ag?
It's an adoreable puppy. For your sake, I wish it was true. But then, if it was, *I'd* be after her, too

I'm sorry ...