Revan doesn't engage in false intrigues; that's something to remember.
If a son is disgraced, he is truly an heir.
If a daughter is kind and sweet on the outside, she is truly a bloodthirsty maniac on the inside.
From the very beginning, Sonata didn't seem kind and sweet to me. Her concern for the citizens seems too contrived; I think she's going to establish a terrible tyranny here.
Added 14 minutes later
Sonata seemed like a good girl who had no chance of ruling (without the death of one of the heirs), although she looks like the best option. It turned out that she is a good girl who doesn't rely on "chances."