Cove, we travel everywhere with our 16yo daughter, who is paralysed from the chest-down.
Re flying, any airplane is no trouble at all. Make sure to ask that she keeps her own wheelchair right up to the plane... what they then do is transfer her into an aisle chair which they keep on board during the flight. Her wheelchair goes into the hold (if you're very lucky they may be able to squeeze in onboard - more likely in first, and preferable because they've been known to damage chairs in the hold) and is then brought to the door of the plane upon disembarkation.
We've done this in all kinds of planes, mostly in Y, sometimes in J. Using the bathroom is the only tricky bit, but that won't be an issue on a short flight.
You don't need a wide-bodied plane because they won't let her use her regular wheelchair on board anyway... they'll make her sit in an aisle chair which the FA's or special assistance staff have to push to her seat. So any plane is fine.
Note that if you're in Y, they'll want to board you first, and you'll also be last to get off. But in F I imagine they may let you off early... provided the ground crew are quick-smart with the wheelchair, which they're often not.
Re car transfer, any car will work provided you can stick the wheelchair in the boot. But because cars with high ground clearance don't allow for a straight transfer from chair to car seat, try to avoid an SUV. A Lincoln town car should be absolutely fine, especially if she's got a wheelchair that folds up with removable wheels. Probably the perfect car for a wheelchair user is a station wagon/estate... but they're not very popular in the States. But put it this way: we use NYC taxi's no problem, so a Limo will work fine. Just remember, if you want to have her transfer herself into the car with no lifting, go a car with the least amount of ground clearance.
Oh, one last thing: never take this girl to Bali. We tried it with our daughter once, and even though the airline knew we were travelling with a wheelchair passenger, the airport was hopeless and helpfully didn't arrange for an aerobridge so I had to carry my daughter down the slippery metal steps to the tarmac in the rain. And do it all again on the way up a week later. A bigger issue with loss of dignity than anything else, but to be avoided.
Any other questions, just fire away.