How can I politely tell my cousin that I don't want to play this game with her anymore?

I have been playing Words With Friends online with my cousin regularly for several months. I have beaten her twice out of hundreds of games over that period of time, and both times she was really crabby about it, and made a bunch of excuses about why she lost. Also, she has made multiple comments that lead me to suspect that she is cheating, and once even admitted to using a word finder. She complains when I take “her” spot for a word, she yells at me for blocking the board or making a space she wanted inaccessible. She is in her 50s, but I swear sometimes it is like she is throwing tantrums.

I guess, in short, she’s a very poor sport. I guess I am, too, because I am tired of losing every day. It’s not fun to play like this. The problem is that I still want to play the game, I just don’t want to play it with her. I tried just avoiding her, but she kept sending me requests. I don’t want to just come right out and say that I don’t like playing with her, my intentions are not to hurt her feelings… I just, well, don’t want to play with her. :\