or can his girlfriend file for change of status after she's been in the US as a non-immigrant for a few years?
It depends on the type of felony that your brother was convicted of. He should speak to an experienced immigration attorney in his area.
Attorney answers to questions are for general purposes only and do not establish an attorney-client relationship. Please contact at the Law Office of Daniel Corno, (832) 767-2922, 1535 South Richey, Pasadena, Texas 77502 email@example.com, elabogadodaniel.com
Because of the Adam Walsh Act US citizen is ineligible to file a petition for immigrant status under INA 203(a) or nonimmigrant K status, if has been convicted of a "specified offense against a minor," defined in section 111 of the Adam Walsh Act as an offense involving any of the following:
(1) An offense (unless committed by a parent or guardian) involving kidnapping;
(2) An offense (unless committed by a parent or guardian) involving false imprisonment;
(3) Solicitation to engage in sexual conduct;
(4) Use in a sexual performance;
(5) Solicitation to practice prostitution;
(6) Video voyeurism as described in Section 1801 of title 18, United States Code;
(7) Possession, production, or distribution of child pornography;
(8) Criminal sexual conduct involving a minor, or the use of the Internet to facilitate or attempt such conduct; and
(9) Any conduct that by its nature is a sex offense against a minor.