Who was miss liberty on us coins?

It depends on the coin to determine who the model was.

For example, the Peace Dollar had Liberty modeled after the designer's wife Teresa de Francisci. But the Morgan dollar was modeled after Anna Willess Williams.

"Liberty" never meant a real person, but rather a personification of the ideal of Liberty, a bit like the gods and goddesses of ancient Roman and Greek coinage.

The US didn't want to be like the European countries and put people on their coinage, instead they wanted to put ideals on them. Rather than be lead by a king or a long-dead hero, they wanted to be lead by the ideal of Liberty.