Lera wouldn't really regret it. It definitely gives her some advantages but the idea of sending Vati to murder someone clandestinely sits very poorly with her. It's not even that Vati would definitely mind -- she even offered! -- but she's worry it could poison their friendship or make it a business thing. She'd rather be able to not feel guilty about what she has to ask Vati to do. With the spellswords, there's a military arrangement that makes it easier. Asking an assassin to murder someone is under the table and basically criminal.

Not to mention that her boyfriend's a paladin (THE paladin, in fact) and her best friend is an assassin. She worries about that too.

Will Vati want to meet Missie when the opportunity becomes available? Especially since Lera could set that up.