In order to bring your adopted child into the US once adoption is complete, you must have several things happen. You should have an experienced ADOPTION attorney/agency coordinating this for you
If your state gets involved in the adoption process (a few do not if it is international), you will likely need to contact the appropriate state agency (Children's and Family Services, for example, in WI) that would provide an approval to the INS on your behalf. They may not require a home study because she is a relative, if they do, you must get one. See what they will need your dossier to include.
You will also need to apply to the INS for a visa (I600? Check and see for sure) and have a legal professional in Samoa handle the Samoan portion of the adoption process there. I do not know what the Samoan requirements are, but most dossiers will, at minimum, need certified copies of birth certificates, marriage licenses, proof of income and employment, proof of citizenship, criminal background check of all parties living in your home, local police clearance, some sort of financial statement (proof of assets and ability to support adopted child), a written statement by the adoptive parents about themselves and why they wish to adopt, photos of the home environment and potential parents.
The child must be a legal orphan under the definitions applied by the INS and Hague Convention.