After getting rid of all the members of the royal family, she took over her kingdom as its new ruler. Obviously it was not something easy to do as she faced opposition from various sides. As Alexandria was still quite young, she was very inexperienced in the matters of politics even though she had many souls who were experts in this matter to take help from.
So instead of taking risks with her limited and theoretical understanding of politics, she did what she found to be the perfect solution in the current situation. She destroyed all her oppositions with overwhelming power. That way she was able to stabilize her ruling in a very short amount of time.
At first she was known to be a tyrant and everyone was scared of her. But as she grew up, she became more adept at ruling a nation and proved herself as a ruler with very high qualifications. In just 5 years, she went from being a tyrant to a wise queen.