Jumping off of this, not only is there a lack of interest, but the few times we've ever seen her, that lack of interest turns into a general desire not to be anywhere else. I doubt Khet is particularly bright, but even she knows Phil's community is going to be a mixture of detractor memes that either call her a horse/gold digger/a cheater or reference her weird ass family stuff. Of course she's going to appear sullen and miserable. The only other things we really know about Khet come from pretty unreliable sources.
I don't think she has much of a personality though. She seems like she's just content to do her own thing and live as Phil's roommate. Leanna was actively trying to make Phil change. I certainly don't believe everything he said that was a result of Leanna's actions, especially the psot breakup stuff, but I do believe that he was actively scheduling time off to be with Leanna because she complained and was trying to save the relationship.
With Khet, there's really nothing that obvious which makes me think they barely spend anytime together, which she is perfectly okay with. He only invokes her name when he wants to deflect responsibility or do something he thinks would make him look bad to own up to. The one thing I can really think of that was a Khet decision is making Phil take a Tuesday off recently. That seemed legitimate just because of how he clearly was unhappy with the schedule change and made such a big deal out of it.