Unfortunately, no one has the insider info on exactly 'how' the IRS is going about this.

It appears it was 2018 first, by order of lower to higher income.  THEN on to 2019, if filed.  And again, lower income to higher incomes..

I've heard of folks having to enter the spouse info (n/a in your case) instead of the taxpayer, issues if PO BOX vs PO Box, need to enter zero even if there was a refund, especially if there was an underpayment penalty, yada yada yada.

My 2 cents on your sister's situation is the change in filing situation probably blew the computer's mind & hers was punted to the back of the line.

Sorry, I know that doesn't help at all if she's strapped for cash.  Neither does the fact the money will get to her eventually with the filing of the 2020 return in 2021.

Too, too many folks that NEED the money aren't getting, yet dead folks are.   The IRS *was* tasked with an almost impossible situation, during adverse conditions...  I actually have (gasp) some sympathy for them.