Once she had herself admit she was a liar, all she said can be taken as a lie.

I'm sorry, but you're taking this to an extreme that I just scratch my head at. She said it to a greedy capitalist who's looking out only for his family's interests. Context is important.

She's lying about there not being other expeditions - she knows there's always a chance for others to be there.

Do you consider the Doctor a liar (and therefore would have to hold to your same standard) since he intentionally lied to her when he told Rose that he sang a song and the Daleks ran away?