I interpret it more as Luna getting up in Eiza's face and giving her a warning. I mean Eiza already tried to have MC killed once, and MC is once against putting his life in danger (even though he's going together with a team), in order to save her sister.
From Luna's perspective, I'd imagine MC being put in danger twice, due to Eiza will pretty much piss her off, and worse thing about it is, she (Luna) herself can't be there to protect the MC herself (Hopes has already confirmed that this mission is top secret and classified that neither Luna nor Gracie would be allowed to be on it), which would make it very, very frustrating for her.
Hence, I'm getting the feeling Luna is basically venting her frustrations out on Eiza & either giving her a warning or even threatening her should MC be hurt in any way.
Besides, Eiza's not really one to show that much emotions in her interactions (only person that she managed to open up a little bit is the MC), so I doubt she'll be the one to be "in your face" to Luna (also, DeLucas are the ones who are helping get her sister back, so it wouldn't make sense for her to purposely try to antagonize one of the daughters of the Family).
Just my two cents of how I see it.