尸 this radical is used as 'corpse' as well, derived from placing an awning or covering over a corpse. In the sense of 眉, the 尸 covers the eye 目.
There is a story that women would remove their eyebrows 眉 before marriage, so you could say marriage is preceded by 媚. I have another idea though, 屓 means to show patronage, but it can also be used in the sense of (~をえこ贔屓する) showing favoritism or (贔屓の~) favorite thing. The 貝 represents money, because they used shells in the old days as currency (as seen in 貨). Most modern uses of money use 金 as gold became the currency standard, but you see 貝 in some more archaic kanji.
This idea of being patronized by a lord under a flag comes from 屓. 眉 can be thought of in a similar way, instead of the covering of the eye, it is the 目which pledges allegiance to the flag 尸, which the women 女 is holding.
woman 女 putting up a flag 尸 so that you may cast you gaze 目 on her.
Or it could simply be the women is raising her eyebrows to your flirtatious advances (or using her eyebrows to lure you in ha).
媚 Flatter, humour, flirt.