Well it depends doesn't it? I mean if she 2+C she will be open to some exhibition, 4+ open to cheating on the MC 5+ open to public sex and then I believe less then 10 C or 10+C (depends on who it involves) then she will dislike the MC being with other women, if it's 10+ / 11+ (again depends, seems it's more okey to sex orcs then humans) she will start to think it's hot, if it's 15+ she will want to join in and if it's 20+ she will join in. So I guess the corruption score is just to low for her to like it... also I believe it was mentioned that there will be a resolution of Kath + Tia (3some hinted) when the 5.3.0 is released.
Also on a side note I think it's funny that the walkthrough has switched at some parts from saying pure / corrupt route to pure / fun route