My Sister 🙄

So my baby is due October 17th and so her shower is in September. Well my sister has told me she wants to also have her wedding in September. And she refuses to move it to another month. Now is it just me being hormonal or is that not a little selfish? I don’t want to fight with her because that’s my sister and I don’t want her to think I don’t support her marriage, which isn’t the case. I already consider her boyfriend family. How do I talk to her about it without coming off as a bi***?