Can employer ask for immigration proof without job offer

Hello, I am on H1B visa and my wife is on H4 EAD. She was interviewing for a job and when the HR asked about immigration status she mentioned that she had H4 EAD and does not require sponsorship now or in the future. HR person got back with multiple requests to my wife in an email 1. Send your H4 EAD card. 2. What is the expiry date of your EAD 3. Send priority date of your your spouse's green card. 4. Were you ever on H1B. etc Her response was that she will send all the required documentation if in fact she has an offer from them and they never got back. Is it legal for an interviewer to ask for actual document proofs before even knowing if they want to offer the job ? Thanks Ashish