... I tried to pay her federal estimate using IRS direct pay and could not do it. ...
The same thing happened to me earlier in the year when I tried to make a Direct Pay payment related to a relative's 2021 federal income tax - couldn't get past authentication despite multiple attempts using various strategies. I gave up and mailed in a check.
The EFTPS website claims one week to deliver a PIN via USPS after you get past the (weak) EFTPS authentication. I recently opened a EFTPS account for a relative so we'll see if the PIN arrives promptly as promised. EFTPS authentication may be weak because crooks haven't (yet) figured out how to make money by paying someone else's taxes.