This
Exactly
i think its a little similar to that. im thought is she knew she was best for that spot and, not in a competitive sense, pushed her brother aside on succession so he could live a more free life. but at the same time, she doesnt understand (emotionally) why her brother is so against her innocent personality disappearing and becoming someone more like her father (which she isnt but to his eyes it could seem that way because his father is apathetic and so is medea)
She had the capability. She is smart and manipulative and thinks outside the box. She is the perfect heir to the Solons. If she can use them all to liberate her brother, whom she loves, from the position that shackles him, why wouldn't she?