Barring a diagnosis that hasn't been shared here yet, flying should be perfectly safe up to the end of the third trimester, where the risk becomes going into labor mid-flight. In fact, unless there's a diagnosed problem with a doctor's order to rest, it's best for pregnant women to stay active. However, if the pregnancy is so new it's possible your wife is in the depths of first trimester exhaustion. I know I was very, very tired and weak for a large part of my first trimester but as the first trimester ended, my energy and ability to eat returned and I was able to go back to my normal activities, and even flew to spend a week out of the country, until the last month or two when I got too big to move around and breathe well (the lungs get squished when the baby's bigger . . . it's harmless but not fun!).
That said, even if the pregnancy is perfectly healthy and you aren't in a position to land together soon, asking about an extension may still be worth doing in case anything comes up later. Pregnancy is unpredictable like that.