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The only connection I can suggest between the swelling of her leg and the mouse was - by her chasing the mouse, she may have slipped or caused apparent injury to herself.
Over the counter medicines and cats do not mix very well because cat's are really sensitive to these products and further problems may result.
You are right in having to get her to the vet as soon as you can get her in, and meanwhile, I suggest you do your best to keep her indoors to reduce any exercise or activity; you can place a warm, microwaved towel or warm heating pad on her bedding to help relieve any discomfort she may have.
I hope her leg heals quickly! I wish there was more we could do for her at home but for now, try the above and have her examined tomorrow!
Good question. I suppose there is a slight chance of a bite causing infection. All animals carry bacteria that can be transferred from a bite...I have not known of a mouse bite to cause this to happen but one never can be sure! Your vet will more than likely xray and draw blood for testing to make sure an infection is not 'brewing' inside your cat.
If you would like to contact me with results when you have time, I would be interested!