I have to admit that her acting kind of jumped around. I thought she did great as War Tasha in YE, but when I saw her as Sela explaining how she was "all Romulan" in Redemption I was somewhat disappointed. Maybe it's the material and directing?
I don't know, I kinda like the idea that in that moment, she is trying to convince both Picard and herself of those words - Her whole life she grew up hating her mother for betraying her father, but now she's meeting these people who knew a version of her mother. As an example, I've grown up hating my deceased father, but if I suddenly found a chance to learn more about him... I don't know how I'd react. So if Sela felt the same... It could be she's afraid that she's going to find her image of her mother challenged, come to realize that her mother really was a prisoner, but loved her enough to try and take her with her.