to win, to have surplus, surname
嬴 centers on gaining an advantage or coming out ahead: winning, having a surplus, or being in a position of abundance. The surname sense is a specific application of this idea of prosperity.
嬴 is a complex character whose exact historical development is uncertain. It likely combines a phonetic element related to エイ with 女 (woman), but the original semantic role of 女 here is not clearly established.
The bottom part is 女 (woman). Imagine a woman surrounded by a complex structure of surplus goods, representing winning and abundance.
For エイ, picture a winner shouting 'A!' (エイ) in triumph, holding a surplus prize above her head.