She's only around at a specific time of day, try looking around 6-12 ish.
This is actually wrong, she's actually supposed to be around all day and night, the problem is if you collect too many npcs at the bar, Piperita gets knocked off the options, I don't know if she just glitches under the North action or what, but what you are experiencing is when Jael'yn goes to bed. If you don't have Jael'yn or Sandre and Caera, Piperita will always be available. It's when you have Jael'yn, Rumie, Nina, Sandre/Caera, Talulah and Piperita the options get overloaded and she won't appear until Jael'yn goes to the barracks. Don't know if anyone has made a bug report, I'll double check but just realized this myself so figured I'd post on this in case anyone was curious.