"A bridesmaid needs to be unmarried" - Interesting...
Webster's 1913:
Maid (?), n. [Shortened from maiden. ?. See Maiden.]
1. An unmarried woman; usually, a young unmarried woman; esp., a girl; a virgin; a maiden.
Bride = woman getting married.
Maid = young unmarried girl or woman/virgin.
In contemporary American culture it's just friends/family of any age/marital status. But they really should change the name.
If the word "literally" in the vernacular, has come to mean the complete opposite of its original definition, let's not begrudge the word "maid" losing its original marital status -- and it's more about their virginity IIUC -- connotation.
English is just a mess.