My cat was hit by a car but she's walking and grooming — do I really need to take her in?

Go tonight, not tomorrow morning — she needs to be seen now. A cat who walks in after a car strike is not a cat who escaped injury; she is a cat whose adrenaline is doing the talking. The injuries that kill after road accidents are the ones you cannot see: bleeding into the abdomen, a torn bladder that leaks urine into the belly over the next day, bruised lungs that get worse for 24–48 hours, and a tear in the diaphragm that lets the gut slide into the chest. Cats hide pain brilliantly and shock masks it further, so a cat who seems fine is exactly what we expect, not a reason to relax.

Move her as little as you can. Slide her into a carrier or a firm box rather than lifting her under the belly, support her whole body, keep her warm with a towel, and let her lie however she chooses — do not straighten a limb, do not pull at anything. Give no food and no water, because she may need sedation or surgery. Note the time of the accident and, if you know it, which side was struck.

On arrival they will check her gums, her breathing and her belly, and they will usually want x-rays and to keep her in for observation. That observation is the whole point: the picture at hour one is not the picture at hour twelve. Your vet will weigh what the exam shows against what the imaging and bloods show, and that decision belongs to the hands on her, not to a guess from a distance.