Somebody on the group text said the walker will fit in the back of the SUV. It might. But the number on the box is a folded size measured under ideal conditions, and it does not tell you whether the device will get through a tailgate on a wet morning. Before anyone agrees the car will take it, do the test you would do for any piece of furniture you are not sure about: bring the actual device to the actual car, then fold it, load it, and unload it.
Local option: New Plan Care gives families in the St. Louis area in-home help so a parent can stay home: companionship, help with bathing and dressing, meals, and overnight care. Call (314) 405-0887.
Measure the opening, not the trunk
The number that matters is the smallest opening the device has to pass through. In most cars that is the hatch or trunk lid at its lowest point, plus the lip of the bumper, not the flat floor behind the seats. Write down three measurements: the width at the narrowest part of the opening, the height from the bumper lip to the roof of the opening, and the depth from the back edge to the seat back or wheel well. Then measure the device in the folded state you will actually lift it in. A wheelchair with the footrests still attached is a different object from one with them off, and the footrests are often the part that catches on the frame.
Check the lift as well as the fit
A device can fit in the trunk and still be a bad job. Ask the provider what the device weighs folded, then lift it from the curb to the trunk floor three times, the way you will on a rainy morning with a parent waiting inside. If you have to lean in and twist to get it in, that is your answer. Say it out loud. If the weight or the reach is more than one person should take on alone, the plan needs a second person, and that is a line item too. This is general lifting sense, not a substitute for advice from your parent's care team, so ask the therapist or equipment provider what they recommend for folding and lifting that specific model.
Check the passenger seat, because that is the real transfer
The trunk is only half the job. Every trip also depends on getting your parent into the front or back seat with the device out of the way. Sit in that seat yourself and note where the door opens, how high the seat sits, and whether the device would have to ride in the back, which in many cars means folding a seat down or sliding the front seat forward. Ask the question you would ask about any new route: who has to move what, and who is standing at the curb when it happens.
Write the line items
Every trip has a load step, a drive, an unload step, a wipe-down, and a return of the device to the house. Put each one on the list with a name beside it. The person who drives is usually the person who lifts, and that is how the labor quietly lands on one daughter. Decide who loads on appointment days, who covers when the first person is at work, and who cleans the car after a muddy or wet trip. If the device has a part that comes off, such as a seat, basket, or wheel, name who removes it, who reattaches it, and where the part lives while it is off.
Before you buy or borrow
Ask for the folded dimensions and weight in writing, along with the list of parts that detach. Ask whether the model you are considering folds smaller than the one you already have, or whether a different style would suit your car better. If the device is coming from a loan closet or a local program, ask whether their measurements are for the folded device or the box. The Local help page lists places in the St. Louis area to start asking. Keep the measurements in the same folder as your parent's other papers, so the next person who drives already knows the answer without asking.