For tonight, you can massage the foot to give her some relief. You can also soak the foot in warm water with epsom salt.
Tomorrow, you will need to see the vet to have it checked out. This could be an allergic reaction to an insect bite or it could even be from a snakebite.
No matter what, you need vet intervention to help her get through this, particularly since there is a smell. This often indicates the need for antibiotics.
Let me know if you still have questions.
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