Size of table
It is harder to adjust up than to adjust down, but I have seen big table players that play worse on a Barbox than the big table. On a big table, players have a tendency to play halfway close position, which ends up with them missing. On a barbox, lots of the time, you have to play pinpoint position.
If you are a money player, then get the size of table you make the most money from, and shim it up. Otherwise, probably get the 9 footer, but beware, cause your wife may not shoot any better on the big table, and continue to hate it. Position play on a 9 footer takes a stronger stroke, and she may be limited on her stroke.