How do you find a federal criminal defense lawyer if a person is convicted in 1 state and lives in another?

I believe you will need an attorney licensed to practice in the federal district court where she was convicted as well as the appellate court for that area (for Mississippi it's the 5th Circuit) should it be necessary to file an appeal.

I would strongly suggest contacting such an attorney quickly as you have a limited time to file an appeal.

Using facts from both of your questions, the conviction was already entered, and she has already been sentenced, with a surrender date on August 18. Under these circumstances, time is of the essence, she needs to get an application filed for the assistance of the federal public defender in Mississippi so the appeal can be filed on time. After that, she can seek to substitute counsel if she is dissatisfied with the services she is receiving.

Sites she (or you) can check out in regards to pro bono in Mississippi include:
http://www.probono.net/ms/
http://www.mslegalservices.org/MS/index.cfm
http://www.nmrls.com/mvlp.htm
http://probono.uslegal.com/mississippi/

Good luck.

DISCLAIMER
Since I do not practice law in your State, this answer is provided solely for informational purposes only, for you to use as a starting point when speaking directly with a lawyer in your State. This answer does not constitute legal advice, create an attorney-client relationship, or constitute attorney advertising. I urge you to immediately contact an experienced criminal defense lawyer admitted to practice law in your State before you make any decisions about this case.

I agree that she needs to promptly see and retain an attorney in the district in which she was convicted!