Not exactly the same situation since passport is in maiden name so you're not asking to change her name w the airline, but perhaps you'll have luck submitting paperwork in writing to indicate the 2 names belong to the same person. From delta.com:

Name Change
The member's signature and SkyMiles membership number must be included in all written correspondence. Name change requests cannot be processed over the phone. A copy of supporting legal documentation (e.g., court order, marriage certificate, divorce certificate) must be submitted by fax/mail and will be required for any name change requests.


Fax: 404-773-1945
Phone: 800-323-2323

Mail:
 Delta Air Lines, Inc.
SkyMiles Account Support
Dept. 654
P.O. Box 20532

Atlanta, GA 30320-2532