Those "persecutors" better be agents of the state (government) and not just common criminals.. Or at least criminal gang that sister's home country government is either unwilling or unable to control.. Our office is very experienced in asylum cases.
When sister presents herself at the port of entry, say San Ysidro (avoid Otay Mesa) between Tijuana and San Diego, she could be paroled in or temporarily taken into immigration detention, for a few days, to enable the Los Angeles Asylum office dispatch an asylum officer conduct a "credible fear" interview of sister in detention. If the officer can establish, based on your sister's oral testimony, that there is more than 10% chance that what she suffered persecution, then she might be paroled into the country to pursue her asylum claim affirmatively with the asylum office or might be NTA'd for immigration court.
Best wishes to your sister.
Behar Intl. Counsel 619.234.5962 Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
I would add that if she is a victim of severe domestic violence, there is case law (Matter of RA) that might support that claim. As you are in the Los Angeels area, you could contact our office to schedule a consultation at 818-541-9999.