Let me guess

Its not Ryute she after but the throne itself. I bet. She just wants to be the queen and have the power that goes with it.

So just another B who is drunk and obsessed with power

I don't think that's particularly wrong tho, in their noble society the queen's seat is the highest she could achieve and probably be satisfying her family (father). As she gets the seat, she finally has some more power of her own. And especially in a society where women are expected to be nothing more than agreeing servants - it's her last straw
So I get where she's coming from ╮(￣▽￣)╭
And honestly I wouldn't be too accepting either in her position of a happy go lucky former non-educated commoner whose main quality as a queen is to be madly in love with the king
After all, all of the noble ladies have been suffering their whole lives by the suppressing court, (manners being always obeying, to men) and not having any freedom of their own

I agree on some points on the nobility part and I do feel bad for her on the pressure her father gives her. But MC isn't just some uneducated commoner and also not just getting the position because she loves the king though. She is is still a noble(although illegitimate) and is a saintess that protects their country. She may not have had a chance in noble studies and etiquette. But has contributed more than a noble lady that has only had their family title to their names. Added to the fact that MC has protected the king numerous times during their subjugation missions in his days as a knight.

Plus the vibe Melanie gives from what she says and the ways she approaches MC and ML is that she does not like her personally. She would constantly tell her to change the way she holds herself in saying that it will make ML uncomfortable. Even when the ML openly says she loves the way she is. She would also greet and look at the ML with affection even though the ML says they don't associate much. Overall it just gives the feeling that Melanie is jealous that MC is the one who receives such love from ML in general.

I've not read the novel so I might be wrong on the last part. But from what I've seen in the new chapters. She is constantly using the ML's name in "reprimanding" MC in front of other noble ladies when the MC is now to be in a higher position than her entourage. They openly humiliate her and Melanie just lets them. You would think that a noble would be more refined in the knowledge of current societal standings and know how to use double entendres in addressing and "reprimanding" MC but they don't.