。
I am in touch with the girl's keen sensibility.
Literal
Girl [attributive-の] sharp sensitivity [at-に] is-touching-[continuous-ている].
A somewhat literary sentence about emotional/aesthetic attunement. 感性 ('sensibility, sensitivity') is a noun for one's emotional or aesthetic faculty — distinct from 感情 ('feelings, emotions'). 触れる ('to touch') takes に for what is being touched (both literally and figuratively). Figurative ~に触れる ('to come in contact with X') is used for being exposed to ideas, culture, or someone's inner world. ~ている marks the ongoing state.