syntonic -- Gretchen

syn·ton·ic  (sn-tnk) adj. 1. Psychology Characterized by a high degree of emotional responsiveness to the environment. 2. Electricity Of or relating to two oscillating circuits having the same resonant frequency. [From Greek suntonos, high-strung, intense, attuned, from sunteinein, to draw tight : sun-, syn- + teinein, to stretch; see ten- in Indo-European roots.]

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Gretchen is an unusually syntonic and exuberant child.