I don't know why you would feel bad telling her not to come over If she has the nerve to do what she did, then it should not hurt her feelings for you to tell her she is no longer able to use your pool. There are consequences to behavior - and she has to have a consequence for her insensitivity to your wishes. You are not being mean - you are the opposite - you are stopping her from taking advantage of you, and your kindness, and if enough people called her on her behavior maybe she would learn something and people would want to have her around. As it stands, I am sure many people run the other way when they see her coming.