Now I'm not saying that I want her to have been jealous. I'm just curious why any jealousy in that direction wasn't emphasized. K/Janelle consistently had a better relationship than K/Christine, even when they were at their best. They had the Vegas "Renaissance" with more romance while Christine’s relationship was going down and up and down. In Flagstaff, he was spending more time at Janelle's house and was trying to be there comparatively more. They also had a good sex life while he and Christine struggled with physical intimacy.
Yet the closest I can find to Christine expressing jealousy of Janelle was during the beginning of her breakup where she talked about how hard it was to see K with R and Janelle and how unfair it was that he got to be intimate with them while she had no one. After that, Christine focused on pushing Janelle to leave K. During one scene, she tried to focus on how bad things were, but when Janelle revealed that K was visiting her in the trailer, Christine moved to a different angle.
I'm glad Christine and Janelle have a good relationship and that they're able to be the nucleus of the family. I just find it curious.