Injury from a car, person or something else could be the reason yes. If she has a lot of muscular soreness, many times this can take a few days before it really feels bad to move around.
If she is vomiting, cannot control her bowels or urinary functions, or becomes unresponsive, you should take her into an emergency vet clinic tonight.
If she is eating and drinking (with your assistance) and seems to be stabilized, she should be fine until you can get her in first thing tomorrow. Take a very close examination of her entire body for bite wounds - especially around the neck, back, ears, throat and face. It's easy to miss something like this so check her out thoroughly.
For now, if she isn't displaying any of the emergency signs above, you can give her one regular adult aspirin now and before bed time tonight. It's best to try and give her this with food. (NO TYLENOL, ADVIL, ETC ASPIRIN ONLY!) Also put a warm towel (microwave it) OR warm heating pad on her bed to lie on. (Place the heating pad under a towel so she is not direclty on it and use with supervision only). The aspirin and heating pad will help relieve her discomfort.
I hope she does well and recovers quickly. Take care,