When to call regarding a second interview for a job?

I had a job interview last thursday at a Pediatric Office and it went very well. She said she liked me and though I would fit in great, and she said she would call me on Monday regarding a second interview. Monday came and she didn't call, I called and left a message and still no return call. Today's friday and I still haven't heard from her. Should I call again today, or chalk it up as a lost cause? I really want to job..... Thanks =)