Though it is difficult to predict ovulation time in irregular period, you had involved in sex around expected due date which is very much safe. Here, chance of pregnancy
is almost nil literally and you also got negative pregnancy test.
1-7 days period date alteration is normal thing. To induce period, you can take progesterone
pill like duphaston/ meprate
for 3 days. You get withdrawal bleeding within 7 days.
In spite of taking above medication, if you do not get your period, you need to consult with your gynecologist for relevant investigation & suggestive measures.
In the mean time, she must take balanced diet, avoid stress
, drink plenty water/ fluid, keep bowel habit regular, do yoga/ light physical exercise, eat carotene
based vegetables and take sound sleep.
Be well & always practice safe sex.