Daily Hero Battles have been cycling through the same 10 or so units since the very first day. If you’ve missed Olivia, she’ll be back soon.
I tend to prefer Reposition on units with high defense, since they become the new front line unit. I put Draw Back on units with range attacks or low defense, since they can stay behind the front lines. Pivot or Swap goes on armoured units so they can advance further than one space.