For Elizabeth, I am inclined to believe that she didn't file the proper dual-status nonresident return for 2018 and that was probably what triggered the EIP.  Had she filed the proper return, I doubt the IRS would have sent her any money at all.

As for Americans overseas, I was surprised that Congress decided to use AGI instead of MAGI, which would be more common for this type of tax credits and didn't change that before the bill was passed.  They must be feeling generous.