hiiii marcie i love your videos <3 as for your question, i had to think back a bit, i considered this to just be stated as canon outright? the ep 8 manga, and one of eva's lines in ep 7 tea party at least from what i remember heavily implies it, but i guess it is just that; heavily implied. either way i've always considered this to just be straight up canon :') and yeah it makes me want to tear my hair out (/positive) it perfectly shows how self sacrifical eva can be for the ones she loves, not talking about something so deeply traumatizing to anyone (not even therapists, just in case) because she cannot risk it being spread and ange finding out. instead she just writes it in her diary, to keep herself not only somewhat sane, but to keep herself remembering, as she likely began to forget what happened due to trauma (i think the manga at least implies this?). obviously, although she cared for ange, her grief (and from what i remember, her illness as well) eventually overtook her and twisted all of that into something horrid </3

so like, idk if absolutely everyone hc’s evatrice the same way i do, so i guess i should address that first !! my general theory has always been that she’s eva’s inner child (as in the psychology term) physically manifested. maybe i can talk about this again some other time in more detail! still, i think she can be read differently depending on which chapter/scene she appears in. like in ep 3 she also represents the culprit theory, and in ep 8 the lid on the cat box.
evatrice’s relationship with eva is so interesting it makes me want to. scream. i always felt eva grew up quite lonely, and focused more on her studies rather than her friendships. as is mentioned in ep 3, evatrice helped her reach her goals, and encouraged her to work harder towards them. evatrice’s super strict and often cruel towards eva (because eva’s very cruel towards herself) but in a way that makes one think she’s upset, because she knows eva is capable of more. evatrice just reminds me of eva when she was younger, a kid who never felt loved in her childhood home, who had to continuously ‘prove her worth’ to her family, and one who often falls back on bad coping mechanisms to keep herself safe. this is also why i love both eva and evatrice pretty equally.
as for george, evatrice seems to symbolize eva’s helicopter parenting, as well as eva’s way of living through george. if i wanna bring up the inner child theory again, evatrice screaming about how ‘george is her precious son who is not yet grown up’ and how much ‘she suffered to raise him right’ would be eva’s inner child getting out of control, desperately trying to stay in control over george.
listen, i have so much to say about ange and evatrice, but i’ll hold myself back and only focus on a few points asfasjfkas basically, she’s cruel towards ange just like eva is. a lot of that cruelness is real, and some of it might be (MIGHT BE, although i doubt it and am not excusing any of it) manufactured so that ange accepts her as the culprit behind the massacre easier. despite that, eva’s care for ange still shines through even evatrice, as she is the lid of the cat box ange wants to open. it’s no coincidence evatrice’s the one to show up to help ange in ep 8 when she decides to pursue the truth despite everything. even tho she agrees ange shouldn’t try and force it open, she’s still willing to support her decision (“your aunt will always be your ally” and all)
long reply i know, i just had a lot to say. i hope it made at least some sense. anyway, tldr: she’s a scrunckly!!

HOOOO BOY what a loaded question ajhfaksfh,, i could list loads of different scenes or quotes here but i'll stick to the few scenes and quotes that came to mind immediately upon reading this question! those being the scene she has with hideyoshi in ep 1 in the guest room (it's the first clear moment where we see her put down her walls) and the scene in ep 8 where she reunites with ange in the golden land (i have such brainrot over that scene, she talks to ange as if it is 'obvious' she is not worthy of love) as for the quotes, the quotes “your aunt will always be on your side, ange-chan. …… i’ll never let anyone insult your family" and "'she' was my only ally. when things got difficult, when I felt like i was about to get crushed by it all, she would always quietly appear and support me. when I ran into roadblocks and despaired, she would always appear and support me" live rent free in my head