Lucky loser used to be chosen as the highest ranked players among unsuccessful finalist of qualifying competition. Not so long ago ATP changed this rule in such way that lucky loser is chosen randomly from the highest ranked finalists. (Which means that no player can be sure that he will be lucky loser.) See, for example, here.
What are the rules for WTA tournaments? Is there a draw among highest ranked players - as in ATP tournaments - or does the WTA still use the old system, i.e., the highest ranked finalist is automatically lucky loser (if there is a spot available).