Do you know some people that are just contradictory?

basically, I 've got a older colleague who i communicate by email sometimes. I was just telling her that I thought that one of the girls was nasty as she was giggling the whole morning because another person hurt themselves at a sport challenge during the week end. this colleague replied that I probably misunderstood, that she couldn't have said that because she is such a lovely person. I think that she has some nerves because the other day she called her very bitchy. this older colleague behaves like she just says lovely stuff about people while she always slag people off but she doesn't seem to tolerate when people make remarks any idea why people behave this way, saying something and when you agree, they say the contrary? what's wrong with them?