Tatiana allegiance isn't clear to me, but the reasons she made in this chapter really explain why she chose to betray the earth clan, worse yet i... really think that if they had discovered her they would do exactly what she said, the werewolves do care and love their partners but they still do stupid things like having sex with them in wolf form to up the chance of conceiving wolf children, Akira's mom was on a wheelchair during the first series.
Sure there are some that would be against it but unfortunately, i don't think many of them are on the commanding positions of the clan, so her decision really is the only one to exist.