What to do when you're written up?

I got a written warning yesterday for talking/agruing with a fellow co-worker. This is the second time we have been warned, the first was a verbal. However, yesterday was different. I got a phone call and was tol that my sister may have cancer. My co-worker could tell I was upset and asked me what was wrong and I said I didn't want to talk about it. She called me and I said, please leave me alone. She called me again and I said, please leave me alone I don't want to talk about it and I slammed the phone down. There were NO customers around at the time, NONE. An employee who works in another deparmtment told my boss about this and we were written up. I want to go to my bosses boss about this situation because it's not like I did it on purpose. I was having an extremely bad day by finding out my sister may have cancer and I hope she can see that you are entitled to have a bad day and take this warning out of my file. I do not think that having a family issue like this warrants a write up especially when in the write up it says the co-worker who reported us asked "what's going on?" so she didn't know what the situation was. Do you think it's worth an appeal to my bosses boss and do you think she may take this out of my file given the situation?