My mom

So my sister tells me today a conversation that she had with my mom the other day---

It went something like this:

Mom: So what's Sharon going to do for baby stuff?
sister: She'll have a shower or I'll throw her shower.
Mom: But she has a baby.
sister: She has a 9yr old (ftr, Austin will be 10 when this baby is born)

And then my sister said that she just made a snicker like it was the most ridiculous thing she ever heard.

I have issues with my mom to start with and this just p*ssed me off for some reason. This is Bill's [our] first child, can his family/friends throw a shower to celebrate without being frowned upon because I already have a child?

Am I being petty or blowing this out of porportion?