Wench used to mean young girl, so if you find someone describing a lovely wench in Shakespeare, it means a lovely girl.
Wench comes from Middle English, and was a common word for girl, child, or servant. Over time it came to mean mainly serving girls, as in a bar wench, who serves drinks at a tavern. Eventually it came to mean prostitute. If you find wench in a love poem from the 16th century, think of it as an informal version of maiden. But if someone called you a wench last week, you should be insulted.