Is it just hormones?

I’m currently pregnant with our second and wondering if I’m just extra annoyed by this situation because hormones or if I’m justified in being regular annoyed. My MIL often refers to our son as her baby, this has always annoyed me and I’ve brought it up to my husband but never felt the need to say anything, he has even jokingly corrected her or said something about his younger brother who is technically her baby. My son got stung yesterday and she texted this morning asking how her baby was doing and I just wanted to fly off the deep end. I almost texted back ‘idk what (her youngest sons name) is up to today’. In the grand scheme it’s not a big deal it just drove me so crazy today!