MonStar is considered to be a lot more timid and shy than Star. Constantly being bullied, called a ligger and mostly rejected by her own people caused her to shelter herself in more.
Less time spent with guards learning the intricacies of neck snapping and more time spent with daddy Toffee learning about the kingdom.
So she'd likely either never even try making Marco break out of his shell and get with Jackie.
Or if she did, she'd likely not actually do anything about it and quietly accept it. As she does her fate.