Welcome to HRM,
As you mentioned that her last period was delayed by 20 days, which suggest that she has history of prolonged interval between periods.
When did she finish her last pill. You must wait for 10days after the last pill to see the period. As you have done repeated pregnancy
tests and all are negative, period will come. If it do not come even after 10days of the last period, just repeat again the pregnancy test. If still negative then your Doctor will give you combined oral pills
. At the same time she has to undergo some other blood tests also ro rule out any cause for her delayed or irregular period.