confused over sister in laws actions. Can anyone tell me what their opinion is?

[dancegirl]

My SIL and I don't get along. Recently I found out that I was pregnant with my 4th child and as we don't talk with the SIL because of various reasons we decided that we wouldn't tell her. On friday she found out from a mutual friend. She hasn't had sexual relations with my bil for three months or more. (he tells all of his friends). Then according to my BIL after she found out on friday she had sex with him Saturday morning and then Sunday morning. (Which he was so excited about he told all of his friends again). Do you think that the news of my pregnancy is spurring her on to become pregnant again with her third child. She vows that she doesn't want anymore but she is the kind of person who would do something petty like this and pretend it was a mistake or do you think that she thinks that because I am getting sex then she should be getting it to she is an extremely jealous person of me I don't know why. She envies my life for some reason not to say my life isn't rather good