美幸 (Mi-ko):
* Mi: beautiful, pretty
* Ko: happiness, luck, fortune
* Combined: "Beautiful happiness" or "Beautiful luck"
恵子 (Meiko):
* 恵: blessing, grace, favor
* 子: child
* Combined: "Child of blessing" or "Gracious child"
Other possibilities:
* 明子 (Mei-ko): "Bright child"
* 美江 (Mei-ko): "Beautiful river"
Ultimately, the exact meaning of "Meiko" will depend on the specific kanji used to write the name.