Explaining Mirellia Hypocritical behavior (if the stroy had logic and actual writing)
I think Mirellia see herself in malty the only different that malty actually fought back which is probably the part mirellia hate the most because Malty is the better version of her but that not what mirellia is mad about she hate malty because Malty is the better version of mirellia but not "the better" that she wanted.
Because in the WN after she send her to the pig king she say "she took the worst of me and her father traits"
The Hypocrite mirellia hate Malty because malty actually is "the REAL better mirellia" not the "incconet better (melty)"
Mirellia hate that malty is like her she even use her ways but the different that malty actually CHOOSE to fight back yes it's a lost battle and impossible but that what makes mirellia even more angry because she know that Malty is literally her if she choose to fight back.
Mirellia hate malty for these reasons
1- Malty is exactly like her manipulative smart and use dirty way to get by in life which mirellia hate because she is a hypocrite because mirellia doesn't want to believe she is a bad person we saw her multiple times trying to play "the good person" even though she know well she is worser than malty and equal with a scum like the pig king which is why she raised melty to be the opposite of her completely "incconet and fair" because mirellia want to convince herself that melty is who mirellia herself really is a lie she made herself and want to believe but in her dying words she said she is going to hell because deep down she always knew she is a monster.
2- mirellia hate the fact that Malty is her but without the Hypocriteicy side Malty act like she want and know who she is she isn't in denial or trying to play hero in a way she is more "free" than Mirellia which mirellia envy and hate malty for it.
3- also mirellia hate malty friends especially Lesty and that prouply because she never had a real friend and hate the fact that Malty who is "like her" can make friends.
4- also mirellia don't like when malty act cute or to "girly" and she say it's spoiled behavior because she hate the fact that Malty has a fun side to her if she was chill and not trying to survive as Mirellia already decided that malty can't have anything "incconet" in any way in her head because mirellia herself doesn't have that.
5- mirellia never allowed malty and melty to bulid a relationship as sisters because she knows melty will take Malty side which is why she raised melty and even dehumanized malty in melty head.
So mirellia really hate herself more than anyone.
6? I guess? This one is kinda less serious since it doesn't even make sense and it's obviously the author rather than the character (even more than usual because what mother envy her daughter beauty like wtf) I don't know what is with the body shaming stuff twords Malty I mean it's obviously the author begin Misogynistic but since this post is basically me trying to make things canon I guess mirellia just insecure that malty is physically more attractive than her and the way she made a big deal about malty sleeping with Takt and later the name changes.. Maybe mirellia was an actual real slut when she was young and she end up regretting that and she is reflecting this regret twords Malty because malty literally only had two relationships in her life literally just Takt and motoyasu and if we are following the Manga and anime only Takt because she isn't with motoyasu same with the anime yet mirellia over the top reaction is obviously her reflecting her regret twords Malty.