First option:
As a K-1 visa holder, your Fiancé(e) is technically eligible to file for an Employment Authorization Document (EAD) immediately when your she arrives in the United States. However, this EAD will expire when K-1 visa expires, which is in 90 days. It is a waist of both time and money to apply for EAD under K-1 status.
Second option:
As a K-1 holder filing for Adjustment of Status, your Fiancé(e) is eligible to file for an EAD at the same time. Her EAD packet can be filed along with the Adjustment of Status packet and mailed together. She will file as category (c)(9).
Third option:
If your Fiancé(e) did not file for her EAD at the same time as filing the Adjustment of Status packet, she may still apply for an EAD in later time. Your Fiancé(e) will, however, need a proof of having filed for Adjustment of Status. Typically she would need to submit a Notice of Action (Form I-797) stating that USCIS received your packet. She will file as category (c)(9).
You may renew your EAD when your EAD getting closer to its expiration date. You must renew your EAD to be able to work until you become a Permanent Resident (or Conditional Permanent Resident) at which time your "Green Card" will be proof of eligibility to work.
We suggest you to check the processing time of the local office you will be sending your application for EAD to and file at a time equal to the number of days before your EAD expires (usually, it is 90 days).
If your Fiancé(e) cannot wait to work in the United states until your marriage, she can apply for her Work Authorization Card. In order to do that, she would have to submit the following documents:
