Okay, I found this that someone put together… I’ll put my comments in red.
Indiana Jones: Large car with 3 rows of up to 4 people. (might be too much for the young one. Easy enough to request being split up into 2 & 3. You’ll all be in the same car.)
Thunder Mountain: cars on train with 2 per row. (The 5 of you will be assigned 3 rows, all in the same train.)
Space Mountain: cars on train with 2 per row. (Same situation as Thunder mountain)
Splash Mountain: logs with 4-6 per log, single file (Your little one should ride in the double seat in the back row with an adult, provided he hits the 40" mark.)
Star Tours: Large Theater, 8-10 per row.
Autopia: 1 or 2 per car. (Again… you’ll be assigned three cars in a row, you can divide up however you want)
Mad Tea Party: 2-4 per teacup
Haunted Mansion: 2-3 per Doom Buggy
Jungle Cruise: 20 per boat
Small World: boat, 2-4 per row
Pirates of the Caribbean: boat, 2-5 per row
Buzz Lightyear’s Astro Blasters: 2 per car
Family/Kid rides, like the Rocket Jets, Dumbo, Mr. Toad’s Wild Ride, Snow White’s Adventure, etc, have 1-2 per car.
In any case, she’s not going to be put with a stranger if she’s the odd man out.