There are several possibilities for a swollen paw that happened suddenly and these include a fracture (less common if the swollen paw is the only injury), some type of trauma causing soft tissue swelling with no fracture, a bee sting or insect bite that is causing an allergic reaction, a snakebite (depending on what area you are in and if there are rattlesnakes or other venomous snakes in your area), a foreign body (migrating grass awn or foxtail depending on your area), or a bite wound abscess from another cat bite. The best recommendation I could make at this point is to have her evaluated by a veterinarian. Is there a 24 hours vet near you? This would be ideal in case it is an allergic reaction or a snake bite, however if there is not one close or you do not want to take her tonight, I recommend keeping her inside and keeping her in a place that she cannot injure herself further then take her in to see her veterinarian first thing in the morning. The risk in delaying treatment is that if this is an allergic reaction or a snakebite, it will get worse until it gets treated appropriately, so while it is up to you, I have to recommend having her seen tonight to be on the safe side.
When you take her in (whether it is tonight or in the morning), you can expect to discuss things like radiographs (X-rays) to rule out fractures or a foreign body that shows up on x-rays (I once saw a cat that stepped on a sewing needle and it was only discovered when we took an x-ray and saw it on the film. I also recommend pain medication as swelling often is associates with pain and it will be easier to examine it and gather the required information if she is comfortable. Other things that your vet should do is take her temperature and other vitals. If she has a fever, a CBC can be performed to gather more information and help pick the appropriate treatment. If there is a wound, then the should be explored and cultured and antibiotics should be started in the meantime. If it is a snakebite, hospitalization may be recommended depending on how she is doing otherwise.
At a minimum, I would recommend pain medication and antibiotics and you can have her rechecked at your regular veterinarian in 3-5 days of sooner if it is looking worse or she is still painful.
Does this help address your concerns today? If so, I would appreciate a positive rating as this is the only way the website knows that I have been helpful otherwise I am not compensated for my time. If you have further questions or need clarification, please do not hesitate to let me know I strive for 100% customer satisfaction.