I understand from reading the manual that you don't have to change the automatic transmission fluid until the vehicle hits 100,000 (barring some specific conditions that don't apply). My wife however, who is absolutely in love with her "Barbie car"

and would like for me to check the transmission fluid to make sure it's ok. Any guidance would be greatly appreciated and keep me out of the dog house. Just want to make sure it doesn't need any more.
I don't understand why your wife thinks she knows more than you about cars. If she did, then she would be the one here asking this question, instead of asking you to do it. Since you're the family expert, why would she not accept your answer, supported by both the manufacturer of her car and seasoned drivers on these forums that the fluid does not need checking?
Its probably some weird security issue because one time she or a friend didn't get their car serviced properly and had a transmission problem. Or more likely, some snake oil salesman told her she needed a "flush and fill" on her car one time, and she took it as the gospel truth for all cars forever. Whatever the case is, why cater to it?
Can you see the pilot of a plane going into the cabin during flight and jiggling the handle on the exits? "Hey passengers, I really don't think the emergency doors will spontaneously blow off mid-flight, and the control tower agrees, but my wife is worried about it, so I'm just making sure."
She either trusts you, or she doesn't. If she doesn't, then you won't earn her trust by checking the fluid as she asked. If anything you'll convince her that she needs to worry about these things because you don't. Next it will be the differential, then the muffler bearings, then blinker fluid.
Don't let this happen!