MIL is a child.

Megan
So I am looking for opinions/advice. My husband and I had our anatomy scan scheduled on a Friday. MIL asked what time, I told her but said we would like to attend this ultrasound alone so we could experience it just the two of us (which I didn't think was much to ask, considering my parents completely understood) She then proceeds to let us know that's not fair to her and that she assumed she could go (mind, this will be her 7th grandchild, 1st for my husband & I, 1st for my parents) so we brushed it off and said well once we find out the sex we would love to come over Sunday and tell you in person. She's all excited about that, as are we because we would much rather see her reaction in person than over the phone. So Saturday, my husbands sister who lives a few hours away (we don't get to see her often but they are very close) of course she wants to know, so we decide to FaceTime her and it was great. She knows not to tell MIL obviously. We go over Sunday and happen to get there before she and my FIL do. Once they walk in I say "so do you all want to know the sex?" Immediately greeted with awkwardness, no reply really. I continue "it's a girl!!!" With huge grins on both me and my husbands face, then my MIL, without smiling, no hugging, no nothing asks "does your sister know already?" And we said "well yeah because we wouldn't be able to see her in person for a while."
She then continues to complain that she should have been the first to know and isn't happy at all to hear about the baby (keep in mind I'm somewhat blind sighted by this considering my parents are super supportive and know that we will tell them once we see them since they live an hour away, and of course their reactions were super sweet and wanted to know if she was healthy & what not) Not to mention I know my MIL and FIL had been hoping for a boy the whole time (they only recommended boy names, always said "he this, he that", and this whole time my FIL is just standing there twiddling his thumbs) so they showed their disappointment on their faces. The rest of the night is awkward and petty. She hasn't tried to contact me really since, when she usually does a couple times a week. 
Am I wrong to feel annoyed by this insane pettiness? My husband is just as annoyed and is trying his best to deal with her without hurting her feelings. I just don't see why she feels so entitled and lets her pride ruin it for everyone. I mean come on, not even a smile when we announce our excitement over our little HEALTHY girl. I just feel she is making it all about herself (which she has done with different situations multiple times in the past)
I would love to hear your similar stories/advice. Thank you in advance!