It's not that bad to get jealous and it's also longing too cause in her past life she didn't get any love. And this current life, yeah, she experienced love except the experience of being loved by your mom and also she didn't even get to meet her mom because her mom died. Adulting doesn't mean you don't have rights to get jealous of someone getting loved by her mom. I think that scene was about her probably longing and wanting to experience to get loved by her mom.
ur thinking that shes taking it away. She,herself, feels awful for wanting that affection despite having so much. But its honestly, true: nothing can replace a parents affection. Maybe you've grown up with both parents, but it hurts for single parent household children to see what they could've had.
Girl, I know everyone has their own perspective, but thinking about it rationally, yes, she admitted she felt jealous. But did she ever actually act on that jealousy? If she were a real child instead of an adult in a child's body, don't you think she probably would've acted on those feelings?
Just because someone's an adult doesn't mean they're not allowed to feel petty emotions. Being an adult means you're better at recognizing those emotions and choosing how to respond to them. Children often don't know how to process feelings like jealousy, so they act on impulse.
Mabel, however, has the mind of an adult. Despite feeling jealous, she didn't lash out or try to take anything away from Oscar. Instead, she even felt guilty for receiving so much attention from both her father and the Duchess.
So rather than reducing her character to "she's jealous," maybe try looking at the full context. She's a much more nuanced character than that. And if she still annoys you, that's fine, you already said you dropped the series. No one's forcing you to keep reading.

pink haired baby freak should die idc this little hoe is a grown ass woman inside of a child and she's jealous because another kid is getting attention from his own mom??? bitch go away
i really do not like the mc i kept hoping it would get better but she just got more and more annoying