Ahhh, just why does your client not have an SSN?  Since she's married to a US citizen, is she on adjustment of status?  If so, she must have employment authorization from USCIS.  And if she has employment authorization, she should be eligible for an SSN.  In the event she doesn't have employment authorization, she may well have breached immigration regulations and should consult her immigration attorney.

In any case, ITIN is not valid for employment tax purposes (as ITIN holders are not eligible to work in the first place).  Whoever hired her should also have but evidently failed to validate her status as required by law.

If she does have employment authorization but just didn't get around to apply for an SSN, she should do so now and apply for an extension to file the tax return.