Why 조카딸 instead of 계집조카 for the word "niece"?

조카 means "nephew," and 딸 means "daughter," so why does 조카딸 mean "niece" instead of "nephew's daughter"?

My Korean dictionary says 조카 is "the son of a brother or sister," and 조카딸 is "the daughter of a brother or sister." There is no word 조카아들 (nephew's son), so it appears Koreans attached "daughter" (딸) to "nephew" (조카) to make the word "niece," more evidence men come first in Korean society. But why did they attach the word "daughter" (딸) instead of "girl" (계집)? Doesn't "girl nephew" (계집조카) make more sense than "nephew's daughter" (조카딸)?

There are two Chinese characters that mean "nephew": 姪 (질) and 甥 (생). The difference between them is 姪 (질) is "the son of a brother," and 甥 (생) is "the son of a sister," which means both can translate as "nephew." My Chinese character dictionary says the word 姪女 (질녀) can translate as "a brother's daughter" (형제의 딸), which means "niece." Moreover, the character 甥 (생) can also mean "brother-in-law" (처남), so the word 甥女 (생녀) literally means "brother-in-law's (甥) daughter (女)," which means she is also "a sister's daughter" or "niece." Therefore, the word 조카딸 seems to come from the Chinese words that mean either brother or brother-in-law's daughter.

How is 㔖 pronounced?

㔖

Has anyone ever seen the above Chinese character? It was actually created in Korea as a "transliteration character (音譯字 - 음역자), a character used to represent a syllable sound in pure Korean words, place- and personal names. It represents the Korean sound /각/ by taking the Chinese character 加 (가) and adding the Korean consonant ㄱ, which means it was created after Hangeul was invented. So, if Hangeul was already invented, why not just write 각 instead of inventing a transliteration character? The same question could be asked about the transliteration character 㔔 (강).

Below is a link to other Korean transliteration characters:

Korean Transliteration Characters