Is it possible to buy round-trip tickets to Jamaica where the return ticket is counterfeit?
My daughter-in-law says she's now stranded there. Is this possible?
Anything is possible, of course, but it is overwhelmingly, vastly, immensely more likely that this is a scam, and that the source of this email or message is not actually your daughter-in-law, but instead someone else trying to get you to send them money.
In this day of easy Facetime and other video connections, you'll want to have an actual chat with your daughter-in-law to make sure it's her and she's really in need. This SE thread and this ABC News story discuss the issue further.
I do not think this is commonly possible, because Jamaica seems to require proof of onward travel. This means that the immigration in Jamaica will check that arriving visitors have a valid ticket for somewhere else within their visa window (a return ticket or somewhere else outside of Jamaica). Because airlines generally lose money for arriving with passengers who fail immigration checks, they also commonly check before they will even let you onto the plane to get to Jamaica in the first place. Since most of these checks are done electronically, they are very hard to fool. Also generally if you did somehow arrive in Jamaica and then fail immigration, what would happen would be that you would be returned by the next plane back to your original airport.
I can think of some extremely uncommon scenarios, for example if you have a legitimate ticket but your airline suddenly goes out of business (Primera Air), or if you deliberately return your return ticket for a refund; and of course you could be temporarily stranded for weather delays or plane maintenance or anything along those lines.
Conclusion: Unless you already knew that your relative planned to be in Jamaica at this time and have significant conversation with her to verify her identity, this is most likely a scam. (My grandparents almost fell for a scam like this, and fortunately held on for long enough to get in contact with my cousin and verify that he never left home and definitely was not stranded in a foreign country! These scammers are very sophisticated, used details from social media, and even convincingly acted on the phone.)
It is possible, assuming you have a very loose definition of "round trip", for example:
Your second ticket could be pre-sold or "fake", but these days of electronic everything, it seems highly unlikely.
There are lots of other scenarios that may lead to someone being left at the airport or otherwise delayed:
Flight is overbooked and the person is bumped for a later flight. In case the airline bumps a passenger, they are obligated to compensate you (the exact kind of compensation varies wildly).
The flight is cancelled due to technical issues, weather, etc. In most cases the airline will reschedule you as well usually for free.
Immigration / customs issues may lead to detention and delay.
You got stuck in traffic or simply missed the deadline to check-in.
There is very little chance of a genuine "fake ticket" scenario. As David mentions in his answer shown above, this is highly likely to be a scam to get you to send money - especially if it is through an anonymous source like Western Union.
Anything is possible. It's however highly unlikely, certainly if she bought the ticket through an airline or a reputable travel agency.
Most likely then, it's a scam and the email is not coming from your daughter in law but from someone else entirely. Which should be easy enough to check by comparing the email addresses of the sender, reply-to address, and any known email addresses of your daughter in law. She should also have other means of contacting you, like telephone, to verify whether the message was indeed sent by her.
The text of the message is also a clue, does it mention actual correct names and addresses? If not, it's a dead giveaway that it's a scam. If it does, are they correct? If they are, it can still be a scam especially if your and her name are relatively common.
So contact her through other means, verify that it really is coming from her (99% chance it isn't btw, especially if you didn't know before getting this message that she's in Jamaica, most people wouldn't go abroad without telling their family after all. And if they get in trouble while abroad would call their direct family first rather than their in-laws).
I've had a round trip ticket issued by an airline (charter) when all I bought was a one way ticket.
I was puzzled, and I asked - I was told that they automatically issued a return trip to avoid issues at immigration (proof of return ticket or onward travel).
I had not asked for it, I didn't even need it as I had residency at my destination, but for some reason they did it automatically.
I'm not sure how they would handle it, or if it was legal. I suppose, but I don't know for sure, that they would routinely cancel the return leg before its date.
While not strictly counterfeit, or not strictly fake, it indeed was a return flight that I didn't book and that I didn't pay for, and that the airline would never allow me to take anyway.
Whether or not this applies to your situation is hard to tell, but it's not very likely, as the traveler would be well aware of such an arrangement.