I wouldn’t be too worried, but if it were my wife, I would have her see a good hematologist.
With WBC, there is usually an area where it shows the “diff” or the breakdown of the various cell types that make up the “WBC” class.
For example: lymphocytes, neutrophils.
It also depends on how low the value is.
If you DM me a picture, including the diff, I could provide more information.
Understanding, my area is urology, not hematology.