If their American citizenship is revoked and they’re not citizens anywhere else, then they would be stateless. There are international laws to help avoid people from becoming stateless, and special methods for stateless people to claim asylum. But clearly, Trump doesn’t care about international laws.
Supposedly this oven had a (broken) internal release. It also can’t swing closed on its own and needs to be pushed fairly hard to latch closed. And lastly, there is no way to turn it on from the inside; You need to activate it from outside after latching the door.
It was the combination of all three of these things that had people immediately suspecting foul play. Because there’s no way she could have turned it on while alone; Someone else had to have closed her in there and turned it on, and the broken internal release meant she couldn’t escape.