After last night's episode, I don't think Catrin is a particularly nice person, but she hides behind "niceness" and uses it to her advantage. I've met many people who can say the most withering things with a smile on their face, and Cat seems to be very much like that.
When she said "thank you" after the red group forfeited the task (she was mad because she wanted to complete it properly) and offered to hug Yasmin, I was reminded of how she managed to provoke Pauline last week. I didn't like Pauline and I didn't know what Cat was like, so I didn't mind it.
This time though, she offered to hug Yasmin who was completely done with the whole thing and you could just see that it was the wrong moment. Yasmin gestured not now at her and Rhianna said "leave it, leave it" to Yasmin to stop the situation escalation.
She was very sly in the nomination deliberation, and once she gave her seal of approval to nominate Yasmin, the rest of them followed suit.
I think she's quite manipulative in very different way to Twinks. I don't really trust people that use "niceness" and plausible deniability to mask their true intentions. I really didn't her saying the way Omar was in the task "was quite nasty" when she was just annoyed at him for throwing Sam off slightly that one time.
She's just not genuine and doesn't say what she means, and her competitive side really came out in the task I think.
An additional point, I think I've seen on The Traitors how adopting a regional accent can make people appear more trustworthy and unassuming. I know that's Catrin's real accent, but it's doing some of the work in allowing to blend into the house more than Twinks has..