I know I’m going to probably get a question about it so I wrote this as a kind of preemptive measure..
In my story they balance each other out, which is something I think you’ve all noticed. One of the consequences of them having been so deeply in love in the ark is that their characters change from their canon versions. She gets darker quicker while he doesn’t have the weight on this shoulders as much as on the show..
For Bellamy he’s more protective but he knows to give them space when they need it. Knowing Clarke and loving Clarke in the Ark allowed him to share the weight of the secret of Octavia and in turn he’s lighter because of that. Of course that means he’s got more to loose which makes him a bit more vicious than the canon Bellamy. Because while we can argue that Canon Bellamy does care about Clarke and is protective over her this happens over the course of the season. Meanwhile here it’s something he has since before they got on earth.
For Clarke, she’s a bit more damaged at the start of the show. She didn’t just loose her father, she lost her best friend (Octavia), the love of her life (Bellamy) and you could claim that she also lost a woman she respected (Aurora). While Canon Clarke doesn’t like Bellamy kidnapping Lincoln the circumstances here are different. Here she was one of the people traumatized by Lincoln and she was treated a lot more poorly than Octavia. She is afraid of Lincoln but instead of letting the fear drown her it makes her wake up in a way.
Bellamy and Clarke had had a perfect day before it all went to hell, so obviously she’s reeling from that. From the about a day ago we were enjoying ourselves in the art supply store and now he’s close to death and she’s ordering someone’s torture. Clarke adopts a very Bellamy Blake mentality here, it’s not right but it’s what we have to do. But it is a bit about revenge for her, she sees Lincoln as the cause of her recent problems and he almost killed the man she loves, so yes she’s vicious.
We know she can reach those lengths in canon because she did when she killed that grounder without remorse but here it happens a lot earlier because of the circumstances.