Heather has been encoded as Jgcvjgt, which translates to:
J = H, G = E, C = A, V = T, T = R.
This leads us to conclude that TQDGTV, based on our decrypted characters, spells ROBERT. It seems reasonable to interpret Q and D based on two observations; firstly, the name resembles Robert, a recognizable name, and secondly, with C = A, it implies that D = B, while T = R suggests Q = O.
c d e f g (cipher) = a b c d e
q r s t u v (cipher) = o p q r s t