If you haven't already started estrogen it isn't a problem. Pills from 3rd to 17th isn't quite enough days to ensure period will come 4 to 5 days later. I've seen it many times. Her period should come in the next day or so. They should have had her on at least nearly 21 pills. As long as you haven't started estrogen pills all is well. If you have started estrogen then her period and stims need to start asap. Last week I had a donor who was late with her period by a couple of days after bcp and I had to start stims due to Chinese New Year, everything shuts down from 3rd to 7th Feb here. I had her scanned and the dr could tell from scan that her period was going to start very soon. If she has a scan and he can tell the period is just around the corner she can start stims. My donor started and then her period came within an hour. Good luck.