She is sure of how her husband filed, but she was also sure that her return had been filed until she couldn't remember getting a refund or paying a balance due?  Single parents of 3 kids can be excused for some uncertainties.  But meanwhile, what is her marital status?  Coming up on two years of separation, are there any divorce proceedings?  Perhaps some state court agreements on how to file for 2022 and 2023?

But yes, she can itemize.  And while IRS might require her husband to do the same, reports of such audits are rare.  Did he claim the kids?  He might get an IRS notice about that.