1. She believes that the Constitution prohibits both the traveling across, and the residing on, the lands in question.
2. She believes that the Constitution prohibits both the traveling across, and the residing on the lands in question.
3. She believes that the Constitution prohibits both the traveling across and the residing on the lands in question.
There's a rule about commas around a part of a sentence that interrupts the flow, but I am not sure if it applies in this case. This also seems to be a case where different style guides might disagree. Grammar geniuses, please weigh in.
I'm no grammar genius, unfortunately, but I reckon that the sentence flows best without any commas and the meaning is clear without commas. Your first option, to my mind, uses the commas as if the words contained within them are an aside whereas they are very much a key part of the sentence. The second one splits the sentence into two but I think it is one unified thought.
OK, that's about as genius as I can be.