The neuter gender of κυνάριον in Mark 7:27-28 does not stop it from applying to the Syro-Phoenician woman as an insult. Per Smyth (197 b):
Exceptions to the Rule of Natural Gender. — Diminutives in -ιον are neuter (199 d), as τὸ ἀνθρώπιον manikin (ὁ ἄνθρωπος man), τὸ παιδίον little child (ὁ or ἡ παῖς child), τὸ γύναιον little woman (ἡ γυνή woman). Also the words τέκνον, τέκος child (strictly ‘”thing born”), ἀνδράποδον captive.
So, even though κυνάριον is neuter and the woman is feminine, that shouldn’t throw us off. The word is still a very pointed insult, directed straight at the woman.