This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 媐 is uncertain. It visually contains 女 (woman) and 巳, but the original semantic and phonetic roles are unclear.
A woman (女) beside a coiled shape (巳) — perhaps a woman enjoying leisure, but the meaning is too uncertain to build a reliable mnemonic.
For キ, imagine a key (キー) that unlocks the mystery of this rare kanji: key -> キ, but the meaning remains locked away.