Summarizing only the parts that are relevant to this Tsukihime quote, Kiara is sort of a savior by nature, but she was bedridden in a Tachikawa Shingon village deep in the mountains for the first 14 years of her life and this lead her to develop a huge superiority complex, on the thought that "I can't even consider these people human since they aren't trying to save me, while I, a most decent human being, would definitely contribute to saving them".
Then one guy visited the highly isolated mountain community with his civilized common sense, casually brought up how Kiara's disease was actually easily curable, and cured her, only reinforcing her dehumanizing superiority complex. She later became a pro bono online therapist, and formed a cult around her without trying much. It wasn't long before there was mass suicides over people not getting her attention, but at this point she had already long ingrained in her mind that she was the only real human, so she thought these ants killing and dying for her sake was really hot, actually.
Her goal in CCC is kinda besides the point here. What really matters here is that this conscious choice of being a normal fish in a tiny pond instead of fully evolving into a low-tier nobody Maradeva is perfectly in-character for Kiara. Her drive to spread her brand of salvation is very much about her ego, so she would definitely ignore the greater vastness of the universe to stay in a place where she would be treated as a physical god.