娃

女 is the indexing woman radical, originally a kneeling figure with hands folded. It marks 娃 as a person-noun, more specifically a child or young girl, alongside 妹 (younger sister), 妈 (mother), 姐 (elder sister). The radical signals: this is somebody human, female-tinged, often diminutive.

圭 (guī) supplies the sound - initial drifted from g- to w- (via Middle Chinese kw-) with rime preserved as -ā. Same phonetic powers 挂 (hang), 蛙 (frog), 洼 (low-lying), 涯 (shore). Carries no semantic load in 娃 - purely a sound-marker for the wá reading.