Advice please. Millie stopped laying.

Four Goldline ladies now 25 weeks old.  All four laid for a week but then Millie was unwell with a crop problem.  Advice from you wonderful people was followed and she has now fully recovered.  After a further 7-10 days she has not resumed laying.  We have suspected that she may be a little younger than the others as her comb is not so well developed, but as she laid every day for a week soon after we bought them, now she is well I had thought she would recommence laying. I am at a loss to know what to do.  Any advice will be most appreciated.  JohnVW