I think that was her frustration talking. After all she was grilled for hours and hours, she had to relive and retell her story again and again and again - which is bad enough, but the suits were constantly harrassing her about it. So I think it's understandable, given what she was going through.
Speculation: Had Van Leuwen agreed, she would have been taken aback a bit, and then would have quickly regained her composure. And would have immediately given specific instructions. Like don't go into the derelict, just inspect it from the outside, take a lot of explosives, set them up outside, then remotely activate... Then nuke the site from orbit... And of course film the whole thing and bring the footage to her as proof so she can finally sleep well.
That's how I see that moment. Apart from setting up the surprise for the audience that there is a colony there already of course.
You wouldn't necessarily have to land and actually go around walking. You could enter orbit and use satellite imaging to at least verify the existence of the derelict spacecraft.