How did you determine her due date?
What was her breeding date?
When was she preg checked?
What would you like to be concerned about?
7 days over you should be concerned she'll need assistance.
21 days over her due date... then you should be concerned about your record keeping.
42 days over her due date, that she isn't bred and either aborted or never was pg.
Rule of thumb is +/- 2 weeks as stated. And more often a bull if over due date in the dairy industry... seems the heifer calves often come a bit early or on time, but not always.