Angela doesn't really go after prince Cassiel because she knows the second prince is the one with support and is going to succeed the throne. Prob she went after Cassiel last time because she thought he's going to succeed the throne and after she finds out the second prince has more support her main focus shifts, but considering how absorbed Cassiel is even during the execution it's probable she decides to use him. But now that she knows she's to prioritize the second prince, I'm guessing she's planning the way to beat Princess Halys. It's not like Angela entirely ignores Cassiel as a prince(?) but she just finds him inferior to the second prince and the princess as something to be prioritized