Personally, I'm not sure M'ree would be intentionally rude? There's being a bitch to family, and there's insulting a stranger, and THEN there's insulting a powerful stranger that spike the ol' Stranger-Danger sensor.
It wouldn't be realistic unless she's an idiot basically, which she objectively is not.
Now, getting provoked or baited into going off on something? Or even something loosely connected to magic but technically different (like Alchemists extreme and terrible tendency to understate things or the amount of value/pomp he treats all his Uber powerful and highly energetic gear with)...that I could see getting a rise out of a nervous, judgemental, science superiority type.
As for defending Lord L'zoril...look, Dream is kinda an extremely touchy ass right now. Not a bad guy exactly, but not someone you actually want the attention of either. As such, I'd expect Alchemist would prefer to avoid bringing him up as much as possible, or at least leave all Name Invocations to the species that's been actively worshipping him and aren't the guy that interrupted Hypnos' on-boarding interview. Bringing up and talking about Didi is another matter of course, but I'm pretty sure she's the second least likely Endless to actually show up or give a sign behind Destiny? Death is both A) busy, and B) dutiful. Didi does have a soft-spot, but the only times she shows up are both serious and directly related to her job (like when dealing with soul stuff or dying people). Comparatively petty social gatherings don't really qualify.