Stressed about due date

Hello! I am currently 10 weeks pregnant and my babies due date is June 29th, 2017. I also have a 5 month old baby girl who was just born June 3rd, 2016.

Here's why I'm stressing - I know that my babies birthdays will be very close, and that's fine! Its the fact that my sister in laws daughter has her birthday on June 27th! My husband's sister seems like she's salty about me being due in the end of June and upset that there's a chance our kids will have the same bday! I personally don't think its a big deal, I can't help when this baby comes! But shes made comments about how expensive its going to be for her now to shop for three kids in one month, and how parties will be so close and blah blah blah. Like jeez, sorry September is the month my body likes to get pregnant! Ugh. I'm just annoyed and my hormones make me get more annoyed.

If you were her, would you be mad at me too?