you know i don’t think anyone ever told eliza that alex was on that plane like if alex travels a lot for the DEO and to keep up the front of being a lab rat–and considering she’s probably published as well, to keep up appearances and also to be like @ the deo yes I’m still useful–then Alex probably doesn’t tell Eliza every single time she goes out of the country
so there’s a very good chance that Eliza is under the impression that in a way the plane rescue was–the best word here I can think of is almost a whim in that it was a random act of heroism, but not quite because if Kara saved that plane then maybe it was something she was gearing up to do, especially as saving a plane is the first thing that superman did
maybe eliza doesn’t know that the reason why kara finally revealed herself to the world wasn’t because she wanted to be a hero or reveal herself but first and only she wanted to save alex
eliza undoubtedly loves alex wholeheartedly but alex doesn’t exactly talk to her much–eliza didn’t know about alex partying her way to failure, or the DEO, or how she felt about Eliza’s expectations (and once she did she actively and we see continuously try to change her behavior)–so a lot of that Thanksgiving dinner makes more sense with the lense of maybe Alex knowing about Kara’s plan and wanting Alex to stop her for a pre-planned reveal, rather than Alex possibly dying without Kara’s interference.