Why does my cat get so upset when I shower?

Everytime I go into the shower my kitty follows me into the bathroom meowing loudly and trying to get in. When I open the shower door for her and she realizes it's all wet in there and she doesn't really want in after all, she'll continue to sit there and meow loudly outside.
I don't get why she's so upset! Is she worried about me in there or something?

It's closed door syndrome. Luxor has it too.

She's afraid you're going to melt away :-)!

She can't understand why you are in there getting wet voluntarily - it doesn't compute. She wants to be with you, but doesn't want to be in the shower getting wet, so she complains.

Mr. Underfoot used to get very upset about me showering. I have a shower curtain instead of a door, and when I would reach to turn on the tap he would MEOW at me as though to say "WHAT ARE YOU DOING? HAVE YOU LOST YOUR MIND?". Then he would run up to me and try to take my arm/hand gently with his teeth and try to pull me away to rescue me from the running water. I had to put him out of the bathroom so I could shower in peace. He gradually learned to accept it - now he just lays on the floor mat in the bathroom while I shower and watches me with a bemused expression on his face.