Name spoiler-Family drama

My sister has been very mean of late towards me and her most recent act was to announce the baby name my husband and I picked. We were keeping it a secret and she knowingly told family members in a group text. She claims innocence saying she didn't know it was a secret but that is a lie. She had to get the name by going through my phone when I wasn't looking. I only know that because I caught her in the act. My mom instructed me to let her handle it but she isn't doing anything about it. The baby is due March 22nd and I want this drama dealt with before then. Otherwise I will have to deal with it when the baby is here and I don't want that sort of negativity around when I am having my first couple days with the baby. I'm not in the best place with my mom either because she has been absent this whole pregnancy and has been unsupportive in this issue with my sister. In fact I think she has been playing both sides. Here is a little back story. When I first got pregnant my sister was meh about it. That was when she started trying for a baby herself. There were no plans for a baby or anything until the moment I announced I was pregnant. In fact she wasn't even engaged yet. So skip ahead a couple months and she is pregnant. Yay pregnant sisters! Not so yay because she lost the baby at 8 weeks :(. This was at the beginning of January, couple weeks before my baby shower. Which she apparently planned on hijacking into her own baby shower/baby announcment/genderannouncment. In the end she didn't come, but she also instructed everyone she could not to come in support of her (as if I am some bully she needs protecting from). So my mom has been saying my sister is acting this way because of the loss of her baby, but I am pretty sure my mom has been going around saying to people about me "oh just ignore her because shes hormonal at this stage of the pregnancy". Which is not the case, and is really insulting to dismiss my feelings especially when I have good reason to feel this way. So I am at a stand still. How do I resolve this before the baby comes? I don't want anyone there when I go into labor if they are just going to make me feel terrible. Even after I don't want them there if this isn't solved. I won't be able to see past their fake joy and fake support and I'll just get mad at them when I should be enjoying my time with my baby or focusing on having the baby. Any advise?