1) HDDR is ticketed 7-days before the event.
2) In most cases, tables will accommodate the party on the ressie.
3) If you have a 2-person ADR, then you usually get a 2-person table.
. . . at the time of ressie, you may take a 2-person table
. . . others may take 4-person or larger tables
. . . there may be no other 2-person tables available
. . . if you are at a 4-person table, WDW can see it on the ressie
. . . so, if there is room at your table, it is seen immediately
4) There is no way to just bring her and fit her in on your 2-person table.
5) You need to have the ADR for 3-people.
6) As mentioned above, try
. . . a different day
. . . a different show time (9:30pm would be a good effort)
NOTE: I have assigned tables at HDDR many times, and it is hard to just fit someone in. I have seen several folks turned away when they thought they could just show up with added people. Quite embarrassing for those extra people who had to wait outside. You might try calling the day of the show, just in case there is a cancellation.