미영 as a whole is not a particular word, but the individual characters have a meaning.
For 미, they almost always use 美 (beauty), as you have also mentioned.
영 may be one of 英, 永, or 榮. These are hanja, or Chinese characters mapping to 영.
英 means flower, excellence, talent; 永 eternity, journey; 榮 glory, honor.
According to a name database, the above three are the most common, in that order
If it's the first one, your sister-in-law's name means "beautiful and talented" for example.
미 and 영 also happen to be the character for America (미국, 美國) and England (영국, 英國).