In Elle's case, she mentioned the lethal measures because she's... not used to using non-lethal. She's more more more than happy to learn and to do them, but she's from a post-apoc world full of mutated animals that will try to eat you and raiders hopped up on drugs. She's used to the method of "try to talk them down, if that fails, self-defense = kill them before they kill you."

ALSO. Something that occurred to me that she'd notice, once talk of tranquilizers came up. She's not the greatest at science, but she is familiar with animal science, and she'd know that different animals on Earth will react to the same chemical in different ways, sometimes even lethal. So... She isn't sure chemical tranqs would be a good idea? Unless there's someone on the crew super super familiar with the Caducans' biology. 'Cuz otherwise, the tranqs could, at best, not work at all, or, at worst, kill them on accident.