Urgh, you have my sympathy MrsS. My MIL thought it was her God given right to know the gender and the names...she would have bet her house we were keeping the gender from her on purpose (but we didn't even know). She also wanted naming rights...yeah sure.
With DS we did know but we certainly weren't letting on. She bunged it on again, and we fobbed her - again. She was ropeable when she found out that we did tell one person, and she told another (my uncle and godfather and her husband who sadly took that info to his grave not 24hours later). She wanted to know why she hadn't been important enough to tell....