
Wait.... SPOILERS WARNING
That is weird. I have read the novel in japanese and in my version Yuri's mother was a foreign spy who instead of "doing her job" has fallen in love with a noble man. She was indeed kicked of the castle and lived in poverty until she died from illness. Yuri, before her mother's death, asked the former "spy" network to give them medicine in exchange of her services but it came too late. Yuri stated that at that time she didn't felt particularly sad for her mother's death, she just felt pity for her. Eventually she joined the spies because she was "too cute" to rot in poverty the rest of her life. She was never in the side of the first prince, she wanted ever the second prince to be on the throne and easily manipulated by her and the other country or the country to be invaded and being given a better noble title. Because her mother downfall had been to fall in love, she swore to herself that she will never make the same mistake. And she managed it because even if Edward (the second prince) died to protect her she still wasn't sad for him never heartbroken. Has for the plot twist of Dean being the first prince, even in the novel we learn it right after the party when Iris was invited by the queen.

Well, if you don't mind spoilers...
Yes. The evil plan was discovered and both the second prince and Yuri were considered as traitors. He died in a fight but Yuri was captured and sentenced to death. Her last wish was actually talking with Iris one last time. Of course, it was't exactly to make friend.
apparently the spoiler i posted before was the wrong one but am gonna leave this up here so that you can see the better one.