cats neck is fat today and she has a runny noise

my cats neck is fat today like it is fury and fat what could it be?

Unfortunately, there is no way we can tell you what is wrong with your cat via the internet.  Did you feel around her neck to see if you can feel anything?  Doe she wear a collar?  If so, did you check to see if it's too tight? Does she go outside?  Could she have been bitten by a snake or some other insect or animal?   If something is looking out of the ordinary, how is she ACTING?  normal?  If she is ACTING different, that is the major clue that something is wrong. 

Sometimes cats will "puff" their fur up to look bigger if other animals are around that they don't recognize.  Of course, that doesn't account for a runny nose. 

If you suspect anything is wrong with your cat, then the best thing to do is take her to the Vet.  Better safe than sorry.