As @Fr8dog stated, this is against the law. If your daughter presented her valid, unexpired conditional, physical greencard when she was hired, she is not subject to reverification and the employer has no right to ask to see those documents.
She should be filing a discrimination claim; employers need to understand the law.
From USCIS Employee Rights page https://www.uscis.gov/i-9-central/employee-rights-and-resources/employee-rights
Your employer may not:
Ask for specific documents because of your national origin, ethnicity, immigration or citizenship status, race, color, religion, age, sex, disability, or genetic information, or because of any other protected characteristic. For example, your employer may not:
Ask for a document issued by the Department of Homeland Security because you are not a U.S. citizen.
Ask for a U.S. passport to prove you are a U.S. citizen.
Refuse to accept your document or refuse to hire you because of an unfounded suspicion that your documentation is fraudulent. For example, your employer may not refuse to accept your identification and unrestricted Social Security card because you have limited English proficiency.
Treat you differently than other applicants because you have, or your employer believes you have, a particular citizenship or immigration status.
Ask to see documents showing your permission to work before hiring you, or before you complete Section 1 of Form I-9.
Refuse to accept your document or refuse to hire you because your document expires in the future.
Limit jobs to U.S. citizens unless U.S. citizenship is required by law or government contract.
Ask you for a specific document when reverifying that you are authorized to work. You may present any documentation either from List A or from List C of the Lists of Acceptable Documents to demonstrate that you are still authorized to work.
Retaliate against you. For example, employers cannot fire you, decrease your pay, or otherwise try to punish you for:
Contacting the Immigrant and Employee Rights Section (IER) in the U.S. Department of Justice’s Civil Rights Division, or the Equal Opportunity Commission for assistance or to file a complaint.
Complaining about discrimination or otherwise asserting your or another’s rights.
Participating in an investigation or lawsuit on behalf of an alleged victim.
Employers should not reverify:
U.S. citizens and noncitizen nationals;
Lawful permanent residents who presented a Form I-551, Permanent Resident Card or Alien Registration Receipt Card for Section 2, including conditional residents; or
List B documents.
File a claim:
https://www.uscis.gov/i-9-central/employee-rights-and-resources/filing-a-discrimination-claim
I understand she wants to be gainfully employed, but the employer has no right to be insisting on seeing the card, especially if she has either presented it in the past or has 2 other qualifying pieces of identification that meet the I-9 requirements. The physical permanent resident card is not subject to reverification; a temporary I-551 passport stamp is under certain circumstances.
https://www.uscis.gov/i-9-central/form-i-9-resources/handbook-for-employers-m-274/70-evidence-of-employment-authorization-for-certain-categories/71-lawful-permanent-residents-lpr